Support DocumentDropEditProvider (#12025)

[jonah-iden]

What it does

resolves #12025
this implements the vscode extension api for

• DocumentDropEdit
• DocumentDropEditProvider
• as well as the corresponding registration method in the language namespace

also implments DTOs including converters and ability to resolve the file Data for those for #11776.

How to test

here is a small test extension:
documentdropedit-test-0.0.1.zip

or you can build it here:
https://github.com/jonah-iden/documentdropedit-test

1. install extension
2. execute "Register dropEdit provider"
3. drop one or multiple fils into editor
4. should see messages with name of each file and content of one file should have been added to current cursor position in the editor

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[JonasHelming]

@jonah-iden @msujew : What is the state of this PR?

[jonah-iden]

I have applied all suggested review changes. So if there aren't any other comments this could be merged

[msujew]

I'm happy with the changes, looks good to me 👍

• The sample extension works as expected with the new API
• The inversion of file system <-> language services plugin dependencies works as well
• The comparator status report marks the API as fully supported

I'll merge this PR in the coming days, if there are no objections.