This needs more discussion - is collapse state metadata or view state?

#100308

Fix #99203

Fix #102049

* notebooks: ensure preloads load before webview output is shown

This serializes code in the webview so that we make sure preloads load
before rending output. Since the rendering of HTML can be deferred,
we also potentially need to defer other actions like clearing and
focusing.

* fixup! rm debug code, comment

* notebooks: pipe renderer API postmessages to the renderer itself

Previously the postMessage on acquireNotebookRenderer API was just
a proxy to the global vscode postmessage. Now, it's linked to the
renderer and will cause an optional `onDidReceiveMessage` method on
the renderer to be called.

The message still _also_ goes to the global webview message handling
for advanced use cases, but this change allows the webview<->renderer
communication to be more nicely contained
and separate for most use cases.

* wip

* fixup! pr comments

- Get rid of output focus sink when cell has no output, to avoid a dead spot when tabbing through cell
- Fix the toolbar losing focus shortly after tabbing onto it, by avoid context key churn
- Fix domFocus when focus is in a different element from the one that is selected (depends on an earlier PR in listCommands.ts)
Fix #99782

Change "Cursor Move Down" commands to more generic "focus next editor" commands, add keybinding to move down out of output, and add context key for "output is focused"

Fix #94159

Fix #99110

- Infinite loop in syncing focus/selection where the view cell index is not the same as the model cell index
- Error thrown when dragging just above the top of the list

Fixes some cell commands when a child of the cell row is selected

#97841