When setSelectionString is called during editing of text (like inserting
or deleting a character), it catches layout in a semi-consistent state
where horizontal position of individual characters cannot be determined.
Therefore during such events, we cannot pass the correct screen position
to the call to UAZoomChangeFocus.

So let's do the UAZoomChangeFocus call after this iteration of run loop.
This ensures everything in layout that had to update has updated when
calling UAZoomChangeFocus, thus enabling us to provide correct horizontal
screen position.

This makes Zoom support avoid doing all 2 conversions between UTF-8 to UTF-16,
and replaces call to rect_for_range with call to rect_at_index, which is
more efficient.

Note that this is a typical micro-optimization not resulting from any
actual performance measurement, but just from a desire to have a lean
code not doing redundant work.

Use `performSelector:withObject:afterDelay:` instead of dispatch_async
for `UAZoomChangeFocus` (Zoom focus change notifications).

Remove extra newline after a method