@FlaggedApi: Enforce using constants instead of literals

Enables a lint that forces useing @FlaggedApi(..Flags.FLAG_FOO) instead
of @FlaggedApi("...FLAG_FOO"). This avoids the potential for typos
causing APIs to not ship as intended.

Bug: 322505144
Test: make checkapi
Flag: EXEMPT lint only
Change-Id: I3a78d918a38927b74c68a216cebf4b5bb692cbfa
4 files changed