Fix missing position updates to blur regions

The PositionUpdateListener sometimes gets called after the
FrameDrawingCallback, because there is no ordering guarantee between
these two callbacks. This causes the BlurRegions sent to SF to
not have up-to-date positions. For example, an empty Rect gets sent
as the blur region bounds, because the position update hasn't arrived
when the surface transaction is sent. When the position update arrives
it set the correct bounds, but it requires another draw to happen so
that the correct position is picked up.

This CL fixes this issue by saving the blur regions that were last sent
to SF in FrameDrawingCallback and sending another transaction when the
position update arrives. That transaction is merged into the previous
one for the same frame, so the final transaction sent to SF has correct
values.

The CL also moves the FrameDrawingCallback registering logic entirely in
the BlurAggregator in the first onPreDraw. This cleans up VRI

Bug: 197239228
Test: atest --iterations 100 BlurTest#testBackgroundblurSimple
Test: atest BlurAggregatorTest
Change-Id: Ia122df40fdf2aa124299461c2e2597b61fa92699