Replace AnnotationAttribute.legacyValue with value

`AnnotationAttribute.legacyValue` is being removed.

This revealed a couple of errors in the tests that also needed fixing:
1. A test used an unresolved `Flags.FLAG_NEW_GEOCODER` reference in the
   `@FlaggedApi`. That is invalid because all flags are resolved and
   replaced with their literal value in signature files.
2. Another test was simply missing some `"`s around the flag value.

Flag: EXEMPT minor refactoring of build tool
Bug: 354633349
Test: m checkbuild
Change-Id: I7317ec23ec80517433c2f7e19e29aff7a15186fc