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)

* adding overlayService

* addressing feedback from UX meeting

* relocating to progressService2

* remove overlayService and update progressService

* partially functioning grid view

* lots of toggling behavior and editor restore

* dimension changes

* restore layout and fix titlebar

* fix view dimensions on toggle/move

* increase timeout for debug config

* undo unnecessary changes to CSS

* put grid layout behind setting

* fix strict null checks

* address code comments from @bpasero

* changing key name

This state is currently unused and make no sense. Update the signature to  prevent ever trying to go into this state

**Problem**
In progress service, the `ProgressState` object is quite difficult to understand. Only a subset of fields are active at a given time so the state is really more like a state machine.

When enabling strict null checks, the existing pattern is also a pain because it is not clear which subset of fields go to gether and will not be undefined

**Fix**
I've been experimenting with writing states much explicitly. This has two main points:

- Encapsulating all state in a single state object (which the progress service already does)
- Encoding each valid state very explicitly in a state machine like manner

For progress service, the encoding breaks the `ProgressState` object up into five different states that the progress service transitions between.

These values are really supposed to be undefined

* Converted another ~70 test files to strictNullChecks

These are the remaining test files that didn't require any changes to non-test file types. I'll send those in separately.

Most changes were automatic and small (`!`s).
The only non-trival change is that `extHostSearch.ts` needs an interface for its test data.

Again used [TypeStat](https://github.com/JoshuaKGoldberg/TypeStat) when possible per #65581. I'm happy to split this up into smaller PRs if you'd prefer!

* Added missing `!`s to `commands.test.ts`