How to overcome the ‘no drag and drop functionality - part 1

public class DragAndDropController 
{
    public String bccAddresses {get; set;} 
    public String ccAddresses {get; set;}
    public String toAddresses {get; set;}
    public String caseId {get; set;}
    public String caseIdChosen {get; set;}
    public String contactIdToEmail {get; set;}
    public String externalComments {get; set;}
    public String htmlBody {get; set;}
    public String subject {get; set;}
    public String textBody {get; set;}
    
    public DragAndDropController(ApexPages.StandardController controller)
    {
        controller.addFields(new List<String>{‘Id’});
        caseIdChosen = controller.getId();
        List<EmailMessage> emailMessages = [SELECT Id, bccAddress, ccAddress, htmlBody, subject, textBody, toAddress FROM EmailMessage WHERE Parent.Id =: caseIdChosen ORDER BY CreatedDate ASC LIMIT 1];
        
        for (EmailMessage em : emailMessages)
        {
            bccAddresses = em.BccAddress;
            ccAddresses = em.ccAddress;
            htmlBody = em.HtmlBody;
            subject = em.Subject;
            textBody = em.TextBody;
            toAddresses = em.ToAddress;
        } 
        
        for (Contact contactsToAnalyse : [SELECT Id FROM Contact WHERE Email =: toAddresses LIMIT 1])
        {
            contactIdToEmail = contactsToAnalyse.Id;
        }
    }
    
    public String goToEmailDragAndDrop()
    {
        String emailAuthorUI = URL.getSalesforceBaseUrl().toExternalForm() + ‘/_ui/core/email/author/EmailAuthor?p24=’ + toAddresses + ‘&p3_lkid=’ + caseIdChosen + ‘&p23=’ + textBody + ‘&p2_lkid=’ + contactIdToEmail + ‘&p4=’ + ccAddresses + ‘&p5=’ + bccAddresses + ‘&p6=’ + subject;
        return emailAuthorUI;
        
    }
}