Add option to prefetch low-resolution tiles

[1ec5]

#7741 adds mbgl::Map::getPrefetchZoomDelta() and setPrefetchZoomDelta() for controlling how aggressively the map loads lower-resolution tiles. This issue tracks adding a corresponding public API to the iOS and macOS SDKs.

@tmpsantos says the optimal zoom delta is 4. Since this isn’t a value that most developers would be able to come up with on their own, we’d expose a simpler, Boolean-typed prefetchesTiles property to MGLMapView.

#9437 is the corresponding issue for Android.

/cc @tmpsantos @fabian-guerra

[1ec5]

@tmpsantos says the optimal zoom delta is 4.

Apparently this constant is defined in constants.hpp.

[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.