Add support for markdown notebook renderers (#115191)

* Use shared webpack version instead of installing locally for simple-browser

* Use npm for building markdown preview

* render markdown in webview.

* update markdown preview height and offset

* Add basic custom notebook renderer point

* update css

* style update.

* update markdown header padding left

* Add example of loading katex to extend the markdown-it renderer

* Rename global to make clear it only applies to markdown-in

* hide/remove markdown preview

* Add wait for initial markdown preview rendering before showing notebook

* Add double click to switch to editing mode

* Fix markdown cells not getting updated after editing

* style polish

* notebook.experimental.useMarkdownRenderer

* switch render strategy.

* Adding very intial drag drop support for notebook markdown cells

* Implement drag/drop stubs for test classes

* Revert unrelated file changes

* Move markdown notebook math to own extension

* Add missing imports

Co-authored-by: rebornix <penn.lv@gmail.com>

extensions/markdown-notebook-math/package.nls.json

@@ -0,0 +1,4 @@
+{
+	"displayName": "Markdown Notebook math",
+	"description": "Provides rich language support for Markdown."
+}