Provide stub(s) for use as system package

[A-Shahbazi]

Is your feature request related to a problem? Please describe. Because of the need for system app permissions(location providing, signature spoofing) now the only viable way to use microG GMSCore is to install the apk on system/vendor partition which is mostly done via magisk modules. These modules are rather bulky and update with every release of GmsCore.

Describe the solution you'd like Providing stub that has minimum needed permissions for GmsCore and GfsProxy saves some space on those partitions, makes updating the needed modules less bulky and maybe less frequent.

Describe alternatives you've considered none

Additional context none

[Fs00]

I'd love to see this! By the way, I've noticed that #1867 is related to this feature request too