For #96436

Caches the custom editors information using a global memento. This makes sure the editor information is available during startup before extensions have been initialized

Fixes #96484

For #77131

For #94408

Moves this out of custom editors

#77131

Fixes #93857

Fixes #94368

Fixes #94383

Fixes #81832

Attempts to support the following cases:

- An file is renamed to now have an extension that is supported by a custom editor

- A custom editor's file is renamed to no longer match the custom editor

In these cases, we try to prompt the user to see what to do

For #77131

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

* 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

* IEditor => IEditorPane

* More panes:
* IVisibleEditor => IVisibleEditorPane
* ITextEditor => ITextEditorPane
* ITextDiffEditor => ITextDiffEditorPane

* imports - remove type alias

* More pane renames
* IEditorService#activeControl => activeEditorPane
* IEditorService#visibleControls => visibleEditorPanes

* More editor renames
* activeTextEditorWidget => activeTextEditorControl
* visibleTextEditorWidgets => visibleTextEditorControls

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`)

Fixes #91703

All custom editors should implement backup or throw an exception if they cannot for some reason.

This allows commands/contributions to enable/disable themselves based matching against the list of custom editors

For #77131

**Motivation**
While our existing webview editor API proposal more or less works, building an editable webview editor is fairly tricky using it! This is especially true for simple text based editors.

It'd also be nice if we could get bi-directional live editing for text files. For example, if I open the same file in a webview editor and in VS Code's normal editor, edits on either side should be reflected in the other. While this can sort of be implemented using the existing API, it has some big limitations

**Overview of changes**
To address these problems, we've decided have two types of webview editors:

- Text based webview editors. These editors used a `TextDocument` as their data model, which considerably simplifies implementing an editable webview. In almost all cases, this should be what you use for text files

- Complex webview editors. This is basically the existing proposed API. This gives extension hooks into all the VS Code events, such as `save`, `undo`, and so on. These should be used for binary files or in very complex text editor cases.

Both editor types now have an explicit model layer based on documents. Text editor use `TextDocument` for this, while custom editors use `WebviewEditorCustomDocument`. This replaces the delegate based approach previously used.

Adds a backup method to the custom editor API proposal. This method allows custom editors to hook in to VS Code's hot exit behavior

If `backup` is not implemented, VS Code will assume that the custom editor cannot be hot exited.

When `backup` is implemented, VS Code will invoke the method after every edit (this is debounced). At this point, this extension should back up the current resource.  The result is a promise indicating if the backup was successful or not

VS Code will only hot exit if all backups were successful.

For #88719

With this change, instead of passing custom editor edit json back and forth with the extension host, we keep the original edit objects on the extension host. This means that we can pass extensions back the exact same edit object they first hand to us. It also means that edits no longer need to be json serializable.

If multiple instances of the same  custom editor are opened for the same resource, the edit stack should be shared between them. This matches how we work with text files