Fix crash after smart selection animation

At the end of the smart selection animation, we run a callback that sets
the selection on the TextView (subsequently starting the action mode
toolbar and showing the handles). However, when the text changes before
the animation finishes, the selection might not be valid, and might get
out of the text bounds, which was producing a crash. This was observed
in a monkey crash. This CL fixes this bug by refusing to set the
selection when the text has changed between the time the animation has
started and the time it ends.

Bug: 69919777
Test: manual testing before and after the fix
Change-Id: Iea043f320004d45ad16dd7e9e5b47e5256e6d9fa