Support NoGapps style package signature faking

Unfortunately due to GMSCore libraries for clients carrying out signature checks on the GMS app,
users are not able to use open source equivalents, and are being strong-armed (by apps) into using
non-free libraries for these functions. NoGapps is an open source implementation of these libraries.

Unfortunately, a patch like this is necessary in order to permit apps to be convinced they are talking
to the closed-source GMSCore. As this "DRM" is implemented at app-level, it's possible to do this,
without the Android OS itself being "fooled" by the faked signatures.

This commit is from the NoGapps project, I am just submitting it on their behalf.
Originates from https://github.com/microg/android_packages_apps_GmsCore

Change-Id: Ic8aaa0728a43936cd4c62382734342ba8f0fbf5b
Merge "Support NoGapps style package signature faking" into du44