Add iOS/macOS observer hooks

[adrian-cojocaru]

Follow-up to #2694. Adds MapObserver events to iOS/macOS delegates.

[github-actions]

Bloaty Results (iOS) 🐋

Compared to main

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.2% +22.3Ki  +0.1% +16.0Ki    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results-ios/pr-3245-compared-to-main.txt

[louwers]

Could you add some example usage to the Objective-C and/or Swift based apps?

[acalcutt]

Do you think this could help troubleshoot #2928 . I was trying to figure out how to troubleshoot the node process crash in xcode but wasn't really sure what hooks to watch for since I have never done it before. Does this add hooks I could watch for?

[adrian-cojocaru]

@acalcutt Using onWillStartRenderingFrame/onDidFinishRenderingFrame might help identify if the problem is inside a frame, but considering your test case has a static map I don't think the existing events will help that much.

[louwers]

Some documentation strings should be added.

[adrian-cojocaru]

Thanks for adding the documentation!