meson: Complete the port from Autotools

The Meson build is a mechanical port from Autotools, and it's failing for a variety of reasons — but, mostly, because it's lacking a coherent policy for the various bits and blobs that each target depends on. There's a fair amount of over-linking, and inclusion paths are leaking all over the place. These issues prevent building Geoclue with Meson on highly parallel build machines, as targets will tend to run out of order.

Switching to a more idiomatic Meson build allows us to clean up everything nicely, and ensures that not only we have the right in-project dependencies satisfied, but we also don't make the build more complicated than it already is.