DocumentWindow removes \n symbols from an inserted string

gistfile1.txt

class UnknownPrefixAnnotator : com.intellij.lang.annotation.Annotator {
    ...
    override fun annotate(element: PsiElement, holder: AnnotationHolder) {
        ...
        holder
            .createErrorAnnotation(element, "Uses an undeclared prefix")
            .registerFix(new ResolvePrefixIntention())
        ...
    }
    ...
}

class ResolvePrefixIntention : com.intellij.codeInsight.intention.BaseElementAtCaretIntentionAction() {
    ...
    override fun invoke(project: Project, editor: Editor, element: PsiElement) {
        ...
        editor.document.insertString(offset, "PREFIX $prefixLabel: <$prefixIRI>\n")
        ...
    }
    ...
}

plugin.xml

<idea-plugin>
    <id>com.sharedvocabs.plugins.rdfandsparql</id>
    <name>RDF and SPARQL</name>

    <vendor
            email="info@sharedvocabs.com"
            url="https://gitlab.com/sharedvocabs/intellij-rdf-plugin">
        sharedvocabs
    </vendor>
    
    <product-descriptor code="PRDFANDSPARQL" release-date="20200301" release-version="20201"/>

    <depends>com.intellij.modules.platform</depends>
    <depends>com.intellij.modules.lang</depends>

    <extensions defaultExtensionNs="com.intellij">

        <errorHandler
                implementation="com.sharedvocabs.plugins.rdfandsparql.diagnostic.RDFAndSPARQLErrorReportSubmitter"/>

        <!-- SPARQL Endpoint support -->

        <toolWindow
                id="SPARQL Endpoint" anchor="right" secondary="false"
                icon="/icons/icon_rdf_grey.svg"
                factoryClass="com.sharedvocabs.plugins.rdfandsparql.sparql.execution.registry.SPARQLEndpointRegistryToolWindowFactory"/>
        <serviceViewContributor
                implementation="com.sharedvocabs.plugins.rdfandsparql.sparql.execution.serviceView.SPARQLEndpointsServiceViewContributor"/>

        <!-- Services -->

        <applicationService
                serviceImplementation="com.sharedvocabs.plugins.rdfandsparql.common.services.PrefixCCLookupAPIService"/>
        <applicationService
                serviceImplementation="com.sharedvocabs.plugins.rdfandsparql.common.services.LinkedOpenVocabulariesAPIService"/>
        <applicationService
                serviceImplementation="com.sharedvocabs.plugins.rdfandsparql.common.services.RemoteOntologyCacheService"/>
        <applicationService
                serviceImplementation="com.sharedvocabs.plugins.rdfandsparql.usageStatistics.RDFAndSPARQLUsageLogger"/>

        <projectService
                serviceImplementation="com.sharedvocabs.plugins.rdfandsparql.configuration.RDFAndSPARQLPerProjectConfiguration"/>
        <projectService
                serviceImplementation="com.sharedvocabs.plugins.rdfandsparql.sparql.execution.SPARQLEndpointManager"/>
        <projectService
                serviceImplementation="com.sharedvocabs.plugins.rdfandsparql.sparql.execution.serviceView.SPARQLEndpointServiceViewManager"/>
        <projectService
                serviceImplementation="com.sharedvocabs.plugins.rdfandsparql.sparql.execution.serviceView.SPARQLEndpointServiceViewLocator"/>

        <!-- Configurables -->

        <projectConfigurable
                id="rdfandsparql.parent"
                displayName="RDF and SPARQL"
                groupId="language"
                instance="com.sharedvocabs.plugins.rdfandsparql.configuration.RDFAndSPARQLParentConfigurable"/>
        <projectConfigurable
                id="rdfandsparql.prefixdeclarations"
                displayName="Prefix Declarations"
                parentId="rdfandsparql.parent"
                instance="com.sharedvocabs.plugins.rdfandsparql.configuration.RDFAndSPARQLPrefixDeclarationsConfigurable"
        />

        <!-- Indexing -->

        <indexedRootsProvider
                implementation="com.sharedvocabs.plugins.rdfandsparql.common.RemoteOntologyIndexableSetContributor"/>
        <fileBasedIndex
                implementation="com.sharedvocabs.plugins.rdfandsparql.common.OWLOntologyPropertiesIndex"/>
        <fileBasedIndex
                implementation="com.sharedvocabs.plugins.rdfandsparql.common.OWLOntologyClassesIndex"/>

        <!-- SPARQL -->

        <fileType language="SPARQL" name="SPARQL" extensions="sparql;rq"
                  implementationClass="com.sharedvocabs.plugins.rdfandsparql.sparql.SPARQLFileType"/>
        <lang.parserDefinition
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.sparql.parsing.SPARQLParserDefinition"/>
        <lang.syntaxHighlighterFactory
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.sparql.highlighting.SPARQLSyntaxHighlighterFactory"/>
        <lang.refactoringSupport
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.sparql.psi.SPARQLRefactoringSupportProvider"
        />
        <lang.commenter
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.common.RDFAndSPARQLCommenter"/>
        <lang.braceMatcher
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.sparql.highlighting.SPARQLPairedBraceMatcher"/>
        <lang.formatter
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.sparql.formatter.SPARQLFormattingModelBuilder"/>
        <annotator
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.sparql.SPARQLUnknownPrefixAnnotator"/>
        <annotator
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.common.annotator.UnknownNamespaceAnnotator"/>
        <completion.contributor
                language="SPARQL"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.sparql.completion.SPARQLCompletionContributor"
        />
        <renameHandler
                implementation="com.sharedvocabs.plugins.rdfandsparql.sparql.psi.SPARQLVarRenameHandler"
        />
        <!-- Will be supported in 2019.3
        <editorFactoryListener
                       implementation="com.sharedvocabs.plugins.rdfandsparql.sparql.editor.SPARQLEditorFactoryListener"/>
        -->
        <actionPromoter
                implementation="com.sharedvocabs.plugins.rdfandsparql.sparql.editor.SPARQLFileEditorActionPromoter"/>

        <!-- Turtle -->

        <fileType language="Turtle" name="Turtle" extensions="ttl"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.turtle.TurtleFileType"/>
        <lang.parserDefinition
                language="Turtle"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.turtle.parsing.TurtleParserDefinition"/>
        <lang.syntaxHighlighterFactory
                language="Turtle"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.turtle.highlighting.TurtleSyntaxHighlighterFactory"/>
        <lang.commenter
                language="Turtle"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.common.RDFAndSPARQLCommenter"/>
        <lang.braceMatcher
                language="Turtle"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.turtle.highlighting.TurtlePairedBraceMatcher"/>
        <annotator
                language="Turtle"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.turtle.TurtleUnknownPrefixAnnotator"/>
        <annotator
                language="Turtle"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.common.annotator.UnknownNamespaceAnnotator"/>
        <completion.contributor
                language="Turtle"
                implementationClass="com.sharedvocabs.plugins.rdfandsparql.turtle.completion.TurtleCompletionContributor"
        />
    </extensions>

    <project-components>
        <component>
            <implementation-class>
                com.sharedvocabs.plugins.rdfandsparql.usageStatistics.RDFAndSPARQLFileUsageTracker
            </implementation-class>
        </component>
        <component>
            <implementation-class>
                com.sharedvocabs.plugins.rdfandsparql.sparql.editor.SPARQLEditorFactoryListener
            </implementation-class>
        </component>
    </project-components>

    <actions>

        <!-- Groups -->

        <group id="rdfandsparql.SPARQLFileEditorToolbar" popup="false"/>

        <!-- Actions -->

        <action id="com.sharedvocabs.plugins.rdfandsparql.sparql.execution.actions.ExecuteSPARQLQueryAction"
                class="com.sharedvocabs.plugins.rdfandsparql.sparql.execution.actions.ExecuteSPARQLQueryAction"
                text="Execute" popup="true" use-shortcut-of="EditorSplitLine">
            <add-to-group group-id="EditorPopupMenu.Run" anchor="first"/>
            <add-to-group group-id="rdfandsparql.SPARQLFileEditorToolbar" anchor="first"/>

            <keyboard-shortcut first-keystroke="control ENTER" keymap="$default"/>
        </action>
    </actions>

</idea-plugin>