This documents the current thinking on the custom editor api. The current api proposal is not actually implemented yet

For #82514

Fixes #81821

This reverts commit 2c1c691b.

This reverts commit 30886e2f, reversing
changes made to 525f1e47.

This reverts commit 2b61a881.

This one was a bit tricky to figure out what was going on, but this is how it
was working before: Terminals that use extension processes calls
$createTerminal from the ext host, this returns a promise with an ID that gets
returned asynchronously after the process has been setup (ie. an ext host process
proxy was created).

The reason we needed the timeout was because the process initialization is async
as we need a layout to occur so that we have the dimensions of the terminal to
give to the process. The fix could have been setTimeout(..., 0) as well but that
feels hacky as well, the fix in this commit is to pipe an event through from
the process manager which is the actual time when we are good to start telling
ext hosts are the new terminals.

Fixes #77655

Preserve comment thread collapse state across extension host update messages, fixes https://github.com/microsoft/vscode-pull-request-github/issues/1400

Part of #81574

Fixes #80375

Fixes #69785

Fixes #69785

Fixes #82896

Fixes #82128