[ios] [WiP] #5036 draggable annotation views

[frederoni]

This PR is still WiP or even PoC as I'm trying to figure out all implications of it and aligning it with #5245

TODO

• Figure out if this solution will work at all.
• Applying transformations is being omitted while dragging which could lead to unexpected behaviour if freeAxes/flat is set.
• Current animation only scales the annotation view, but the most common use case will likely be a pin annotation being lifted. Add this functionality and demo in MBXViewController

_TBC_

/cc @friedbunny @1ec5 @boundsj

[friedbunny]

Not all MGLAnnotation implementations allow for coordinate to be changed, so we’ve been making this mutable only as necessary.

[1ec5]

Should long-pressing an annotation view select the associated annotation and trigger the selection delegate methods (#5130)?

[frederoni]

MKAnnotationView cannot be dragged until it has been selected. So to initiate a drag, you have to tap -> long-press -> pan. Many examples use a workaround to make annotation views draggable immediately after long-pressing by setting the selected property to true in MKMapViewDelegate didChangeDragState, didAddAnnotationViews and didDeselectAnnotationView.

I will postpone this issue due to more critical ( #5127, #5128 and #5129 ) which this issue depends on.
Will take another stab here when selected and enabled is working properly.