[C-1515] Allow repeat pushes via useNavigation inside nested navigator

[sliptype]

Description

Pushing via useNavigation inside a nested navigator (such as a tab navigator inside a stack navigator) was deduping any subsequent pushes to that same screen because the transitionEnd handler was being attached on the inner navigator instead of the stack navigator

• Add getNearestStackNavigator utility
• Use utility to push and attach the transitionEnd handler to the nearest stack instead of the nearest navigator

Dragons

Slight perf implications. I considered computing the nearest stack navigator outside of the performCustomPush function but that would mean every instance of useNavigation is doing that work. I think computing it inside performCustomPush is better and in most cases it will only need to traverse one level up the navigation hierarchy anyway

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Feature Flags

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[amendelsohn]

Ah so that's what was happening. Nice!

[amendelsohn]

should we return navigator in this case?

[sliptype]

I think it's safer to have the consumer explicitly check that there is a result, let me fix up the types so that consumers are forced to check