Do not blur opaque layers

If a layer is opaque, there's no reason to send it to client composition
due to blurs.

Bug: 196828055
Test: atest OutputUpdateAndWriteCompositionStateTest
Test: atest OutputComposeSurfacesTest_SetsExpensiveRendering_ForBlur
Test: perfetto trace
Change-Id: I55461cbad0008351c15e7dd8d2da20e0b1c59f70