Finalize paste api and drop api tweaks

Fixes #30066

This finalizes the documentPaste api. This api allows extensions to attach metadata on text copy and change how content is pasted. Some examples:

- Updating imports for pasted code
- Inserting an image as an attachment in notebooks
- Pasting files converts them to relative text paths

extensions/markdown-language-features/package.json

@@ -15,9 +15,6 @@
   "categories": [
     "Programming Languages"
   ],
-  "enabledApiProposals": [
-    "documentPaste"
-  ],
   "activationEvents": [
     "onLanguage:markdown",
     "onCommand:markdown.api.render",