Improved word break for BiDi pseudolocalizer.

Characted sequences \n and \t are now treated as word separators
by BiDi pseudolocalizer. This solves issues when text rendering
engine breaks a line in the middle of a text chunk marked with
RLM+RLO and PDF+RLM sequences.

Bug:34064580
Change-Id: I52e6018785fae25479fa167440f24c534b0e3253
Fixes:34064580
Test: make aapt2_tests
Test: Run aapt2_tests binary