SF: Fix lifecycle of LayerBE

Use shared_ptr to make sure that the LayerBE object pointed to
by CompositionInfo is not destroyed prior to BE processing
of CompositionInfo structure

Bug: 112259502
Test: cts -m CtsViewTestCases
      SurfaceFlinger_test
      vrflinger_test

Change-Id: Iac647ed3fdc8d41a8c0e00930e89734d0a84eb14