[androidkit] Add SurfaceRenderer utility

Most samples use the same render thread boilerplate -- consolidate as
a utility base class.

Also add Canvas.getWidth/getHeight.

Change-Id: I27c9f51b4fd9d228a39593fbd4650a66d10240c2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/409896
Commit-Queue: Florin Malita <fmalita@google.com>
Reviewed-by: Jorge Betancourt <jmbetancourt@google.com>
7 files changed