@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
diff --git a/api/Android.bp b/api/Android.bp
index cdc5cd1..7326203 100644
--- a/api/Android.bp
+++ b/api/Android.bp
@@ -387,6 +387,7 @@
         "--error NoSettingsProvider",
         "--error UnhiddenSystemApi",
         "--error UnflaggedApi",
+        "--error FlaggedApiLiteral",
         "--force-convert-to-warning-nullability-annotations +*:-android.*:+android.icu.*:-dalvik.*",
         // Disable CallbackInterface, as Java 8 default interface methods avoid the extensibility
         // issue interfaces had previously.