Annotation views now serve as their own accessibility elements. The developer’s own subclass of MGLAnnotationView can customize the view’s accessibility frame and/or path to more accurately reflect the visual hit target.
Add a container view to hold annotations. This gets around a performance
issue with `UIView:addSubview:` where adding views is N^2. It helps
annotation views avoid cutting into callout views when the annotation
views are transformed to be "flat".
This adds an option to MGLAnnotationView so that a developer can control
how their annotation views scale in size as they approach the top of
the map view (along the Y axis). The size change is also affected by
the pitch (tilt) of the map view. If there is no tilt then scaling
is not performed. As the map is tilted scaling is gradually applied.
This turns the MGLAnnotationView implementation into an Objective C++
class so that SDK constants from C++ files can be used.
The new behavior is enabled by default to maintain consistency with
annotations backed by GL sprites. The MBXViewController redundantly
sets the new property as an illustration of use.
