Support for @InspectableProperty on public fields

+ Add a field target to @InspectableProperty
+ Refactor PlatformInspectableProcessor to process annotated fields and
  generate InspectionCompanions that read fields.
+ Require that all inspectable getters and fields be public.
+ Make some hidden getters added to View for inspection public.

Test: atest --host view-inspector-annotation-processor-tests
Bug: 126913705
Change-Id: I0c012f42794885f17a397a2e3dd541b3aa4c2634