Add a more detailed HAL for DISPLAY_DECORATION

Different hardware may prefer different formats for DISPLAY_DECORATION
layers. Add a new struct with two enums: one for the format, and one for
how to interpret the alpha. These two properties are orthogonal.

Add IComposerClient.getDisplayDecorationSupport for retrieving the
struct. I0c2fbc78cf5e4e97cede4762699a1ecc98620919 demonstrates a sample
implementation.

Remove the DisplayCapability.DISPLAY_DECORATION, which is replaced by
this.

Bug: 216644902
Test: manual
Change-Id: I27f119f927b23052c5fd8f068cbca75338fe7b91