Rename and reorganize hiddenapi::ApiList

Change values of ApiList flags to make them easier to extend in the
future and unify naming across all components. Light greylist is now
just "Greylist", dark greylist becomes "GreylistMaxO".

Note that the version code in "GreylistMaxO" must also include any
maintenance releases, i.e. entries on "GreylistMaxO" are accessible
to apps with targetSdkVersion<=27 (O MR1).

Test: m, phone boots
Test: m test-art
Change-Id: I9622e0646eb265008a8bb2652270876ae95dac84