Pause media playback when swiping to the next submission

[vargaat]

What's new?

• The bug was about AV players not being paused on swiping to the next student but I also added pause for webviews as well. The new thing here is the didTransitionTo method in SpeedGraderViewModel.
• Moved pages view controller protocol conformances to extensions for better separation of concerns within SpeedGraderViewModel.
• Added a findAllChildViewControllers method to get all child view controllers of a type and also fixed the existing UIView counterpart method to properly detect when a view of the searched type is a subview of another searched type.
• Added two debug methods to print view and viewcontroller hierarchy. This comes handy when the view hierarchy debugger doesn't show the view tree properly.

refs: MBL-18859
affects: Teacher
release note: none

test plan: See ticket for test submissions.

Checklist

• Tested on phone
• Tested on tablet

[inst-danger]

Teacher Build QR Code:

[inst-danger]

	Warnings
⚠️	This pull request will not generate a release note.

Affected Apps: Teacher

MBL-18859

Coverage	New %	Master %	Delta
Canvas iOS	91.59%	91.61%	-0.02%

Generated by 🚫 dangerJS against 712e4f8

[rh12]

QA + 1

Minor clarification: the media actually stops, not just pauses (which is strange, since the https://developer.apple.com/documentation/avfoundation/avplayer/pause() method should just pause.)
But I think it's good enough or maybe even preferred.

One somewhat related finding: rotating to landscape on iPad (@ iOS 17) the video stops, but this is not a regression.

[suhaibabsi-inst]

Code +1

[suhaibabsi-inst]

QA +1

Tested on iPhone XS, iOS 18.3.1