[google_maps_flutter] Add onPointOfInterestTap support

[tenninebt]

Summary

• App-facing GoogleMap.onPointOfInterestTap API and example/tests
• Depends on published google_maps_flutter_platform_interface 2.17.0 ([google_maps_flutter_platform_interface] Add onPointOfInterestTap support #12752)
• Depends on platform implementations in [google_maps_flutter] Add onPointOfInterestTap platform implementations #12880 (Android / iOS sdk9+sdk10 / web)

Not ready to land until #12880 is published. Path overrides for android/web are temporary for review only.

iOS note: POI taps require google_maps_flutter_ios_sdk9 or google_maps_flutter_ios_sdk10. The default/frozen google_maps_flutter_ios package does not receive new features.

Part of #11872 / flutter/flutter#60695.

Pre-Review Checklist

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• I added new tests to check the change I am making.
• All existing and new tests are passing.

[stuartmorgan-g]

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