Roslyn trims space after syntax node change

ExperimentalRewriter

namespace RoslynFeatureDemo
    using Xunit;

    using System.Linq;

    using Microsoft.CodeAnalysis;
    using Microsoft.CodeAnalysis.CSharp;
    using Microsoft.CodeAnalysis.CSharp.Syntax;

    internal class ExperimentalRewriter : CSharpSyntaxRewriter
    {
        public override SyntaxNode VisitMemberAccessExpression(MemberAccessExpressionSyntax node)
        {
            var rootIdentifier = node.DescendantNodes().OfType<IdentifierNameSyntax>().FirstOrDefault();
            if (null != rootIdentifier && rootIdentifier.Identifier.Text == "node")
            {
                SyntaxNode res = this.Visit(node.Expression);
                var replaced = string.Format("{0}?.{1}", res, node.Name);
                return SyntaxFactory.ParseExpression(replaced);
            }
            
            return base.VisitMemberAccessExpression(node);
        }
    }

    public class RewriterTests
    {
        [Fact] //FAIL
        public void ExperimentalRewriter_AsCastingShouldWorks_Success()
        {
            const string original = @"
public void Express(dynamic node){
    var x = node.A as string;
}";

            const string target = @"
public void Express(dynamic node){
    var x = node?.A as string;
}";

            var opt = CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.Experimental);
            var originalTree = CSharpSyntaxTree.ParseText(original, opt);
            var targetTree = CSharpSyntaxTree.ParseText(target, opt);
            var rewriter = new ExperimentalRewriter();
            var rewritedTree = CSharpSyntaxTree.ParseText(rewriter.Visit(originalTree.GetRoot()).ToFullString(), opt);
            
            // var x = node?.Aas string;
            Assert.True(rewritedTree.IsEquivalentTo(targetTree));
        }

        [Fact] //FAIL
        public void ExperimentalRewriter_AsCastingWithSpacebarsShouldWorks_Success()
        {
            const string original = @"
public void Express(dynamic node){
    var x = node.A        as string;
}";

            const string target = @"
public void Express(dynamic node){
    var x = node?.A as string;
}";

            var opt = CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.Experimental);
            var originalTree = CSharpSyntaxTree.ParseText(original, opt);
            var targetTree = CSharpSyntaxTree.ParseText(target, opt);
            var rewriter = new ExperimentalRewriter();
            var rewritedTree = CSharpSyntaxTree.ParseText(rewriter.Visit(originalTree.GetRoot()).ToFullString(), opt);
            
            // var x = node?.Aas string;
            Assert.True(rewritedTree.IsEquivalentTo(targetTree));
        }

        [Fact] //FAIL
        public void ExperimentalRewriter_CompareShouldWorks_Success()
        {
            const string original = @"
public void Express(dynamic node){
    var x = node.A == 10;
}";

            const string target = @"
public void Express(dynamic node){
    var x = node?.A == 10;
}";

            var opt = CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.Experimental);
            var originalTree = CSharpSyntaxTree.ParseText(original, opt);
            var targetTree = CSharpSyntaxTree.ParseText(target, opt);
            var rewriter = new ExperimentalRewriter();
            var rewritedTree = CSharpSyntaxTree.ParseText(rewriter.Visit(originalTree.GetRoot()).ToFullString(), opt);

            //var x = node?.A== 10;
            Assert.True(rewritedTree.IsEquivalentTo(targetTree)); 
        }
    }
}