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