allow mutation of MGLPolygon interior polygons/holes

[incanus]

Tail work from #6565. If we allow this, we can use the same facility as there to update the annotation on the fly visually.

[1ec5]

At first blush, it’d be trivial to also observe changes to the interiorPolygons key path of any polygon we add to the map. However, note that, since #6565 makes any polygon a shape-shifting polygon, we actually (also?) need to observe the interiorPolygons.coordinates key path. (We don’t have to recurse any further than that: unlike MapKit’s MKPolygon, MGLPolygons can’t contain islands.)

[1ec5]

Pulling into the v3.4.0 milestone. I think it would be highly desirable to ship this issue and #6583 in the same release as #6565 to simplify expectations about what we support.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.