Make text related Paint API public

Following APIs are used by the text stack, and there is no reason for
them to be hidden. Make them public.
- getStrikeThruPosition
- getStrikeThruThickness
- getUnderlinePosition
- getUnderlineThickness
- getWordSpacing
- setWordSpacing

Bug: 112327179
Test: m docs
Test: atest android.graphics.cts.PaintTest
Change-Id: I651a5d620968fedcff2059e0e0694aa4ee770014