Add necessary APIs for supporting glyph level drawing

This CL adds following APIs

Font#cloneWithSettings
  This API provides a faster Font instance creation for different
  variation settings.

Font#getBounds
  This API provides glyph advance and bounding box information.

Font#getMetrics
  This API provides font metrics that will be used for deciding line
  height and/or baseline.

Bug: 168136332
Test: atest FontTest
Test: TreeHugger

Change-Id: I335557ce47ea0ca8e012c2a48b804c00bb348392