Refactor inspector API

- Remove unused IntFlagMapping.Builder#clear()
- Rename IntFlagMapping#namesOf(int) to #get(int)
- Change signature of IntFlagMapping#get(int) to return a Set
- Add doc comment explaing desing rationale to PropertyReader
- Remove IntEnumMapping in favor of SparseArray. Note that this removes
  the immutability gaurantees of IntEnumMapping.
- Miscelaneous doc fixes

Test: atest IntFlagMappingTest
Bug: 122518089
Change-Id: I94acf03431b238d84afcd74cdbdd347431381c40