Refactor Inspector API

InspectionHelper has been renamed to InspectionCompanion for clarity
about its lifecycle. The APIs needed to be accessed from the context of
an inspection agent injected by the profiler have been made public.

With a tightend focus on platfrom views and XML resource IDs, the
@InspectableProperty annotation now has affordances for specifying an
attribute resource ID and for defining @IntDef flag and enum mappings.
@InspectableChildren has been removed, as this will be special cased in
the injected inspector. Additionally, support for attribute ID is now
provided in all PropertyMapper methods.

Additionally, PropertyMapper and PropertyReader now have support for
Gravity ints, @ColorInt, @ColorLong, and Color objects.

Test: mmma frameworks/base
Bug: 120224687
Change-Id: If455e2d1d9693eac39c33fc35f892baf75671ba4