* file model - allow to load a model with contents and use it for working copy move/copy

* remove unused code

* 💄

* more tests

* Investigate to cancel a running save participant when saving again (fix #90509)

* keep token source

Adopt it for untitled and text file models. Use it for indicating dirty count in explorer and document edited on macOS.

web - we need to prevent unload when we detect a pending save or auto save because long running operations are not allowed

This reverts commit 5897b877.

Continues #60565 for converting tests. A few files used TypeStat to add `!`s but the following interface changes were manually inferred from implementing classes:
* `IActiveCodeEditor`'s methods can all return `null`
* `IEditor` needs to report `getControl(): IEdotorControl | null` because `BaseEditor`'s `getControl` can return `null`