This reverts commit a1bb5ac2, reversing
changes made to 9a08a107.

Co-authored-by: NSteVen Batten <sbatten@microsoft.com>

Fixes #46585

This new api allows extensions to contribute webviews to the sidebar or panel

Part of #103120

add ExtHostFileSystemInfo which knows what schemes are reserved and which are used, https://github.com/microsoft/vscode/issues/91697

Fixes #91697

This new API checks if a given scheme allows writing

chore - move appyWorkspaceEdit from extHostTextEditors to (new) extHostBulkEdits and mainThreadBulkEdits

add model version to notebook edits when possible, https://github.com/microsoft/vscode/issues/105283

Fixes #69785

Fix #104958

The serializers belong with the panels, not in their own class

debt - make ExtHostNotebookDocument not implement vscode.NotebookDocument but expose the API object via strict getter

Also fixes message passing for webview views

Add proposed webview view API

For #46585

This adds a new `WebviewView` proposed api to VS Code that lets webview be used inside views. Webview views can be contributed using a contribution point such as :

```json
    "views": {
      "explorer": [
        {
          "type": "webview",
          "id": "cats.cat",
          "name": "Cats",
          "visibility": "visible"
        }
      ]
    },
```

* Use proper activation event

* Transparent background

* Fix resize observer

* Adding documentation

* Move webview view to new directory under workbench

* Remove resolver

By moving the webviews view into their own fodler, I was able to avoid the cycle the resolver was originally introduced for

* Use enum in more places

* Hook up title and visible properties for webview views

* Remove test view

* Prefer Thenable

* Add unknown view type error to collector

Fixes #81007

This removes the initial notebook renderer API and keeps the 'pure'
renderer API described in #102644 and hacked-in previously.

Remaining work in this area, in no particular order:

- Add messaging context to postMessage as requested by Don (API proposal TBA)
- Cleanups around how state is managed internally in the backLayerWebView
- Deprecate the renderer `viewType` in favor of calling it the `id` or `rendererId`

Q: I kept around some of the "transform" functions since the mime type
picking happens there, not sure if there's a better place for this
to happen now, or whether these methods should simply be renamed.