feat: add onCameraFollowLocationChanged callback to NavigationView

[christian-apollo]

Summary

Adds a new onCameraFollowLocationChanged event prop to NavigationView that fires whenever the camera enters or exits follow-my-location mode. This enables apps to reactively show/hide a custom recenter button or adjust their UI based on whether the map is actively tracking the user's position.

Motivation

There is currently no way to know when the user pans the map away from the follow-my-location camera mode, or when it re-enters following mode (e.g. after tapping the built-in recenter button). Apps that overlay custom UI on top of the navigation view (such as a bottom sheet or custom recenter button) need this signal to stay in sync.

Changes

Android — Uses GoogleMap.setOnFollowMyLocationCallback to emit onCameraFollowLocationChanged events when the camera starts/stops following the user's location.

iOS — Tracks GMSNavigationCameraMode transitions via GMSMapViewDelegate methods (willMove:, idleAtCameraPosition:, mapViewDidTapRecenterButton:) and reports state changes. Also fires on programmatic transitions like showRouteOverview and setFollowingPerspective:.

TypeScript — Adds the onCameraFollowLocationChanged prop to NavigationViewProps and wires it through NativeNavViewComponent.

Usage

<NavigationView
  onCameraFollowLocationChanged={(isFollowing) => {
    console.log('Camera is following:', isFollowing);
  }}
/>

Test plan

• Verify on Android: pan the map away → callback fires with false; tap the built-in recenter button → callback fires with true
• Verify on iOS: same pan/recenter behavior
• Verify showRouteOverview triggers false on iOS
• Verify setFollowingPerspective triggers true on iOS
• Verify no callback fires when the state hasn't actually changed (deduplication)

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