Unhide Paint.getTextRunAdvances

This is necessary for getting individual character advances.

The only char[] version of getTextRunAdvances is used, so removing
String/CharSequence versions.

Bug: 112327179
Test: atest android.graphics.cts.PaintTest#testGetTextRunAdvances
Change-Id: Ic49a4742cccb2a5155f6afacef3555e29c7a061c