Clean up TextUtils.doesNotNeedBidi()

One of the signatures of the method that used CharSequence was
unused. The other's implementation was too crude, resulting in too
many false negatives.

The new code now shares logic with BoringLayout in order to detect
potential bidi-affecting characters. The logic is intentionally
rough in order to be efficient: we still have false negatives, but
not as many as before.

Bug: 29254696
Change-Id: I106133369e93e49d7b2fe82ffc433e4556740ee8