Support alpha value in SurfaceView.

For backward compatibility, SurfaceView ignores alpha value by
default. In order to reflect alpha value set on the SurfaceView
to its underlying surface, setUseAlpha() needs to be called.

Translucent alpha only works when the surface is placed z-above.
Otherwise only fully opaque and transparent status are supported.

Bug: 130442248
Test: Manual, use BubblesTest app and checks if alpha is set.
Change-Id: I86847de59109b2adf12a2c7c50c988c2cbcf0450