Apply additional CachedSet rendering fixes

1. Properly set the viewport to be the layer stack content rectangle,
rather than the cachedset bounds
2. The projection space of the output buffer must be stored alongside
the override buffer. This must feed back into RenderEngine when
re-rendering a CachedSet, as the displayFrame of the cached buffer has
to map back into layer stack space
3. The Transform for override buffers must collapse to the IDENTITY
transform, because cached buffers are in the same orientation as the
client target so there's no need to apply a transform

Bug: 180660547
Test: libcompositionengine_test
Test: Youtube fullscreen playback
Test: simulate virtual displays

Change-Id: Ie78c61853b2a712060b5f17045157a457b461cb7