Package libhybris

As discussed in #1039, I want to split feature/hybris branch into smaller sensible pull requests.

This is the first one that simply adds android-headers and libhybris packaging. libhybris allows apps compiled with glibc (musl in our case) to load Android libraries that utilize bionic libc, which is used to load proprietary userspace drivers.

The package isn't very useful on its own and requires core (non-UI/Java) Android services to be running in some way - either in Halium-style LXC container or in same root as main OS with modified init (Mer/Sailfish do it this way). Both ways are tested to work in postmarketOS.

libhybris also includes some tests, not all of them are known to be representative, but test_vibrator and test_egl_configs are usually good indicators if system is set up correctly.