Send transaction callbacks earlier

As soon as layers finish post composition, we can send our transaction
callback so that the client can handle the callback information earlier
before the next SF cycle.  Reduces missed frames.  Also prevents missed
callback if display is not on.

Bug: 152709895
Test: build, boot, SurfaceFlinger_test, libsurfaceflinger_unittest,
manual

Change-Id: I9eff815270f43d1a3b6a0bf7a9c46e17194bd933