[androidkit] Relative-sized cube sample

Update the cube sample to be centered and sized relative to the target
surface.

Also simplify projection handling:

  - pre-compute a full view matrix in onSurfaceInitialized()
  - set the origin to the surface center
  - compute perspective and camera transforms in local coordinates
    (instead of unit view cube)

Also fix (invert) fling Y direction.

Change-Id: I48a3d0b4547812fb3c9b49a9842fb18c0ed0d863
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/413436
Reviewed-by: Jorge Betancourt <jmbetancourt@google.com>
1 file changed