feat: support multiple PointAnnotationManagers per MapView

[mfazekas]

Background

PointAnnotationManager (added in #4209) currently configures the single shared Mapbox PointAnnotationManager instance that all PointAnnotation components use. This means:

• Only one slot value per map — last writer wins if two managers are mounted
• Children of <PointAnnotationManager> are React siblings of the native manager, not routed through it natively, so they all go to the same underlying manager regardless of nesting

What multiple managers would enable

<MapView styleURL="mapbox://styles/mapbox/standard">
  <PointAnnotationManager slot="bottom">
    <PointAnnotation id="a" coordinate={...} />  {/* rendered below buildings */}
  </PointAnnotationManager>

  <PointAnnotationManager slot="top">
    <PointAnnotation id="b" coordinate={...} />  {/* rendered above everything */}
  </PointAnnotationManager>
</MapView>

What's needed

1. Native: Create a new Mapbox PointAnnotationManager instance per RNMBXPointAnnotationManagerView instead of reusing the shared one. The Mapbox SDK supports multiple annotation managers per map.
2. Native: Route PointAnnotation children through their parent PointAnnotationManagerView — make them actual native children so they use that specific manager instance.
3. React: The current wrapper API shape is already correct for this — no user-facing API change needed.

Current API is forward-compatible

The <PointAnnotationManager> wrapping pattern is exactly right for multi-manager support. The implementation just needs to go deeper on the native side.

[github-actions]

Lint failed 😭

Please fix the errors in your code example - More info.:

error: Parsing error: Expression expected at example.tsx:4:43:
  2 | <MapView styleURL="mapbox://styles/mapbox/standard">
  3 |   <PointAnnotationManager slot="bottom">
> 4 |     <PointAnnotation id="a" coordinate={...} />  {/* rendered below buildings */}
    |                                           ^
  5 |   </PointAnnotationManager>
  6 | 
  7 |   <PointAnnotationManager slot="top">


1 error found.```