Adds placeholder cancellation arguments to the custom editor api. These requests are currently never cancelled

For #77131

Adds a hook that lets extensions preserve the webview for a custom editor across a rename

Part of #91606

For #77131

Going back the the delegate based model for a few reasons:

- It gives us a better approach to add additional API hooks in the future (such as for rename)

- In practive, the capabilities were almost always the same as the `userData` on the document. It is rather confusing to have both `userData` and the capabilities 'on' the document

* Use the UndoRedoService for CustomEditors

For #90110

Changes custom editors (the ones not based on text) to use the UndoRedoService. This involved:

- Moving edit lifecycle back into the main process again (this is actually the bulk of the changes)
- Removing the `undo`/`redo` methods on  `CustomEditorModel`
- Using the undoRedoService to trigger undo/redo

Fixes #91700
For #77131

Having an explicit revert method is a helpful signal that the extension should reload the changes from disk

Fixes #22353

StatusBarItem is one of the few places in our API where we only allow extensions to give us a command as a `string` instead of as `Command` object. This change updates the API to also allow passing in a `vscode.Command` (which also allows arguments!)

For #91702

Fixes #92008

Fix #85946

Fixes #91670

- Move model type logic out of `CustomEditorInput` and into two different implementations of `ICustomEditorModel`
- Add `CustomTextEditorModel` that owns a proper model reference to a text document. This should ensure the text document is disposed of if there are no more references to it
- Move most of the previous `CustomEditorModel` into `mainThreadWebviews` directly. This removes some of the indirection that was previously required (such as using `waitUntil`)