and add command to task building progress

Fixes #81636

fixes #71407

Also changes processService to not modify its input actions, which seems like unexpected behavior

These arrays of actions should not be modified by the caller. Mark them as readonly to prevent this. This also let me eliminate a number of not null supressions that had been introduced during the strict null migration

One small code change was required in `showError`. However I believe this was actually a bug since modifying the input array was likely not what would be expected (in practice, we usually just passed in array literals so I don't think we hit this one)

Part of #74250

- Extend `Disposable` in classes where it makes sense
- Use `DisposableStore` for lists of disposables
- Make `combinedDisposable` take arguments instead of an array (so that you can't pass in an array and then modify the array after the fact)