feat(PointAnnotationManager): multiple managers with independent slots & properties (#4240)

* feat(PointAnnotationManager): support multiple managers with independent slots and properties

Each PointAnnotationManager now owns its own Mapbox annotation layer, so multiple
managers can sit in different slots of the Standard style. PointAnnotations
associate with a manager by being its direct children; bare PointAnnotations keep
working via a default manager. A `default` manager can be declared to configure the
slot/properties used by those bare annotations.

Exposes manager-level properties: id, slot, iconAllowOverlap, iconIgnorePlacement,
iconOptional, textAllowOverlap, textIgnorePlacement, textOptional.

- iOS: per-component RNMBXPointAnnotationManager (own layerId), tap/long-press/
  deselect routed across all managers, child mounting in Fabric.
- Android: per-component coordinator (own layerId), click/drag routed across all
  coordinators, child wiring in the view manager.
- Backwards compatible: bare PointAnnotations route to the default manager.

* docs: regenerate examples.json for PointAnnotationManager Multiple example

* example: clearer PointAnnotationManager Multiple demo (spread, labeled pins)

* refactor: trim restating comments in PointAnnotationManager code

* refactor: drop self-evident comment on annotation manager registry

* refactor: drop self-evident comment on annotation parent/owner field

* example: demonstrate slot ordering in PointAnnotationManager Multiple (pitched 3D view)