Rename SegmentIterator to SegmentFinder

Also clean up some helper methods by inlining the logic.

These APIs will be made public in a follow up change.

Bug: 243969224
Test: atest android.text.LayoutGetRangeForRectTest
Test: atest android.widget.cts.TextViewHandwritingGestureTest
Change-Id: I7991ef1f3abdf575b9adc0c5dc971f0cdd09fc87
7 files changed