Preserve tree state in debug Variables view

[haneefdm]

This fixes issues #76427 and #25652 (duplicates). I mentioned in detail what was causing the issue in #76427.

We save and restore the tree state between a stopped->running transition and back to stopped in conjunction with the Call Stack window which keeps track of the current thread/frame context.

It also preserves the visually nice feature of not flashing if those transitions happen quickly (within a half a second) but longer periods between transitions will clear the Variables window (so the user cannot interact with it). The only difference is that if eventually, the debugger stops, we restore the tree instead of going back to the default state.

I tested it with cpptools (MIEngine) and the typescript debuggers.

[isidorn]

@haneefdm thanks a lot for your PR.
This looks good to me. But I think it can be further simplified, can you please try to address my comment. If you think it is not possible let me know and I can look into it.

[haneefdm]

I don't know why all builds are failing. Pretty sure it is not my change that is causing it. How do I restart the checks/builds. I must have done my push exactly at the wrong time.

[haneefdm]

@isidorn I forced a restart of the checks with virtually no change, and this time it only fails on macOS in integration tests (before everything failed during 'Install Dependencies'). Perhaps I should wait for a quiet time and try again. This never happened to me before. Please advise me if there is a better way to start the checks/builds without modifying code.

In the meantime, would it be possible for you to review my comments and the solitary change I made?

[isidorn]

Do not worry about the build failures. Sometimes they fail randomly which seems to be the case now.
I will review your changes today. Thank you

[isidorn]

Thanks a lot for your PR. Looks great, merging in 🎉
I have tried it out and it works nicely!
It even has a nice side effect that if I stop debugging, and start again the variable view state is preserved. I personally like this.
Let's push to insiders to get feedback.

[haneefdm]

Thank you so much. Yes, that side effect was intentional :-) At one point I was looking at the current state of the debugger to save state and then I removed it, because this felt a lot better.

[isidorn]

Great thanks. Yeah it seems good. Let's try it out in insiders and see what feedback comes.