Enable text element editing on Mobile Safari. Big diffs, but all that changed was the click handler is now a function named addEditFormHierarchy and it is now bound to touchend as well as click.
Added support for corner drag to resize on Mobile Safari.

- Moved code from addResizeHandleDragBehavior into BoardDragger, using when the dragged element happens to be the resize element. On desktop, getTappedElementFromEvent uses elementFromPoint, and if clientX and clientY aren't available from the event, it uses event.target.correspondingUseElement.

(Needed to do that because the drag event was being take by the group's drag handler – BoardDragger – on Mobile Safari.)

- Added supporting flags and objects for resize to BoardDragger.
- Increased size of resize handle.
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