[REVIEW 3-6] fdo#52020 use ICU word boundary break iterator for Khmer

[Caolán McNamara]

Rather trivial patch to use the default icu rules for word boundary
detection for Khmer as well as Thai. (we should try and get rid of our
custom line and word-boundary rules but lets be conservative for 3-6).
This makes Khmer spell-checking useful now that recent versions of icu
have lovely new word boundary rules

http://cgit.freedesktop.org/libreoffice/core/commit/?id=8ad1d4443e67784a8c0d3c1a3a72f089cb0cd3ec

C.