Use signature-based trust for package name overrides

Shift the trust model for EXTRA_PACKAGE_NAME overrides from installation status (FLAG_SYSTEM) to cryptographic signatures. Only packages signed with core system certificates are now
permitted to override the calling package name.

Bug: 424853397
Bug: 397217317
Flag: EXEMPT Bugfix
Test: manual
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:cdad9a0002bdcb09fb8594a71169031c910d25f2
Merged-In: I0c337720e42f6492573d261ae66fa88c511cd99e
Change-Id: I0c337720e42f6492573d261ae66fa88c511cd99e
1 file changed