SF: Add Planner flattener

Adds the Planner flattener, which detects when layers are inactive and
flattens them using GPU composition in order to reduce the workload on
the display processor.

Bug: 158790260
Test: atest libcompositionengine_test libsurfaceflinger_unittest
Change-Id: Idc5c2927c8af6fe85653404a7d94c9e68ffc329b
20 files changed