BreakIterator_CTL in the non CharacterIteratorMode::SKIPCELL mode did
not handle UTF-16 surrogate pairs at all, causing backspace to delete
lone surrogates which is really bad. Just copied the corresponding code
from BreakIterator_Unicode.

Additionally, BreakIterator_th was not correctly skipping non-Thai text
and always treating one character as Thai.

Change-Id: Ia379327e042ff602fc19a485c4cbd1a3683f9230
Reviewed-on: https://gerrit.libreoffice.org/54631Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>