Custom editors do not have good error handling when saving fails

[Tyriar]

Context: #115028 (comment)

Repro:

1. Throw in your custom editor extension's saveCustomDocument implementation
2. Debug
3. Open custom editor
4. Make a change, exception occurs on auto save
5. Try close, error notification shows
6. Stop debugging, waiting for dirty editors to save notification shows

Related issue I just created for dirty custom editors with auto save: #115404

[bpasero]

Looks like we still have some specific code for handling save errors that is not generic enough to handle the custom editor, e.g.:

• you don't see any notification when save fails
• the editor does not indicate dirty

[bpasero]

@Tyriar I pushed some commits today that should improve this, can you maybe retry your scenario? Mainly:

• custom editors no longer hide dirty indication on auto save (Custom editors have a hard time implementing isSaving() #115526)
• shutdown is no longer prevented when running from an extension development window (c275946)

[Tyriar]

@bpasero thanks, made a note to try it out in tomorrow's insiders

[bpasero]

Closing as per #115028 (comment) where you can see how this behaves now. The underlying reason why the notification appears and never ends is actually #115588

[Tyriar]

@bpasero much better 👍