Handle deleting non-single-word characters at end of input.  This includes both multi-word code-points and compositions of multiple single-word code-points.

A "backspace" from Android IME will send 1,0 as parameters to extendSelectionAndDelete(...) but it's possible that the last character of the input is a multi-word code and take multiple positions.

The setSelectedRange() call made by setSelectionOffsets() will _reduce_ the range to include only full characters and can end up reducing the range all the way to zero and causing the deleteSelection() call to do nothing.

BUG=355995

Review URL: https://codereview.chromium.org/299123004

git-svn-id: svn://svn.chromium.org/blink/trunk@176961 bbb929c8-8fbe-4397-9dbb-9b2b20218538