Added support for asian characters in text selection.

Inspired by https://review.source.android.com/#change,16606

Test class has been revamped to mimic new behavior: selectCurrentWord
is no longer used to add words to the dictionary. We rely on the suggestion
bar in the IME for that.

Change-Id: I1cb88df54dffb166c75f75fefb743ff55a33519b