Callout anchor for GL point annotations does not account for viewing-distance scaling on tilted map

[1ec5]

The callout view for a GL point annotation has an anchor point based on the height of the image (half the height on macOS). When the map is tilted, a GL point annotation is always scaled based on the viewing distance, but the anchor point doesn’t change with viewing distance to reflect this scaling. As a result, the callout view can be positioned too high when the annotation is far away and too low when it’s near the viewpoint.

This issue has the same root cause as #5694 on Android. It does not affect view-backed annotations on iOS, but #5245 would add an API to mbgl that would expose the map’s transform matrix, making it possible to ascertain the GL annotation’s scale.

/cc @boundsj @frederoni

[stale]

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