Add missing documentation to CompletionItem's insertText

Part of #81574

allow  prepareCallHierarchy to also return an array

Fix wrong key in the extension package.json schema

`appendMarkdown` is now the only way to use ThemeIcons

If we look at the code in vscode.d.ts, we can see that this modes.ts
file is not up-to-date. As a result, monaco.d.ts also needs an update.
Signed-off-by: NRemy Suen <remy.suen@gmail.com>

Fixes microsoft/monaco-editor#1378: Convert view coordinates to model coordinates in getTargetAtClientPoint

Part of #81388

This reverts commit 0dd49ed0.