Eliminate offscreen buffer for some blurs.

For blurs that don't need to crossfade with the original input
we should not need to render the initial input into an offscreen
buffer for sampling.

Test: `atest renderengine_test` and tracing SysUI blurs
Bug: 176903027
Change-Id: I3c6b2782b6d20c260af0077877ebf4720b0e54cc
1 file changed