Consider whitelist when listing class members.

Previously, only the enforcement policy was considered when getting
declared fields or members, meaning whitelisted APIs would still not be
discoverable. Fix this by calling hiddenapi::GetMemberAction from within
IsDiscoverable.

Bug: 77787686
Bug: 64382372
Test: cts/tests/signature/runSignatureTests.sh (with ag/3863796)
Test: art/test.py --host -t 674-hiddenapi
Merged-In: I234d274f47f377e3e105c81aae2d49072287992a
Change-Id: I234d274f47f377e3e105c81aae2d49072287992a
(cherry picked from commit 64ee8aea)