Support WorkspaceEditEntryMetadata

[KamasamaK]

VS Code recently finalized an API for WorkspaceEditEntryMetadata (microsoft/vscode#77728) which facilitates the ability for the client to preview a WorkspaceEdit. LSP should also adopt this.

[KamasamaK]

@dbaeumer Thanks!

What is the reasoning behind making a new interface AnnotatedTextEdit instead of adding annotation as an optional property to TextEdit?

[kjeremy]

@KamasamaK @dbaeumer I was wondering the same thing

[dbaeumer]

TextEdits show up in many other places (completion item, formatting, ...) where an annotation is not supported (and very likely never will be). Instead of documenting this with every use of TextEdit I decided to introduce a AnnotatedTextEdit and use it in cases where an annotation will be handled by the client.