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
 on AOSP wrt merging aosp/3341662 downstream into git_aosp-main-future,
 so merging into that branch first.
Flag: EXEMPT adding flag library
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:ac66333acf283dafc56bb950b5df522d97868405)
Merged-In: I29bb8f9108747a0ed2a1a678811858e8572d285f
Change-Id: I29bb8f9108747a0ed2a1a678811858e8572d285f