[vscode] Evolution of dropMetatada and documentPaste Proposed APIs in VS Code 1.89

[rschnekenbu]

On VS Code 1.89, proposals from dropMetadata and documentPaste have been updated and merged in documentPaste. DropMetadata proposal has been deleted. Support in Theia is partially implemented and partially stubed, some evolutions have to be performed then. This API is used by builtins Markdown and ipynb.