Bug 5250788: LatinIME slows down as amount of Text increases

Removed unnecessary CharSequenceIterator and made the WordIterator
work on String instead of CharSequence

Submit words to the spell checker by batches.

Refactored WordIterator to make it intrinsically local.

Change-Id: Ie9e30691985a130fa55cd052005ddb22a21761cb
5 files changed