fix(core): Add frames back to frame-stack if removed during back press - #11437

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/DevelopmentWorkflow.md#running-unit-tests-application.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

In android 12 and later, root launcher activities are no longer finished on Back press.
However, {N} core overrides backpress and removes frames from stack at times, thinking that the activity will finish.
Then, user attempts to launch the app and it will simply resume without recreating views and frames will still be missing from the stack.

That results in Frame topmost() and getFrameById() returning a wrong frame instance in apps with multiple frames.

What is the new behavior?

This PR uses a workaround in loaded lifecycle to ensure the removed frames regain their place in the frame stack.
Because the stack push function may change the position of an existing frame in it, we make sure to check _isInFrameStack too before acting.

The PR also removes an unneeded override of _popFromFrameStack.

Fixes/Closes #11436.