Add RESERVED_FOR_TESTING_SIGNATURE permission

Now that we support signature permission allowlist in APEX, we can test
it with CTS shim instead of adb remount.

Bug: 308573169
Bug: 309625722
Test: atest SignaturePermissionAllowlistTest
Change-Id: I19073b76266de2ec7833bf09dc8f19cd07acf364
3 files changed