Add keystore2_flags_java-framework

Necessary to flag a new Keystore framework API method (being added in
aosp/3341662).

Bug: 369375199
Test: treehugger
Ignore-AOSP-First: Running into automerger conflict issues
 (https://screenshot.googleplex.com/BF2rGYKdoDQvR2F) on AOSP wrt merging
 aosp/3341662 downstream into git_main, so merging internally first.
Flag: EXEMPT adding flag library
Change-Id: I29bb8f9108747a0ed2a1a678811858e8572d285f