Upgraded MGLMapSnapshotter to be compatible with the latest mbgl.
Converted as many of MGLMapSnapshotter’s instance variables and properties as possible into local variables close to the point of use. The completion handler of -startWithCompletionHandler: and its variants is no longer called as part of -cancel, when the snapshotter is deallocated, or when the application is terminating. -loading once again works and is used to avoid concurrent requests, now that the completion handler is no longer memoized. Snapshotter options are copied and converted into a snapshotter on demand as late as possible.
Made the decoration step synchronous while continuing to perform it on a worker thread. Only access self on user-facing queues. Ensure MGLMapSnapshotter.loading is reset after snapshotting.
Pushed some drawing and completion code up from inner completion blocks to outer completion blocks to avoid excessively passing state around. Converted a few class methods into standalone C functions to emphasize the avoidance of captured state.
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