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.
3 jobs for meson-build-fix in 16 minutes and 37 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Test
passed #12210
ubuntu-16.04

00:10:22

passed #12211
ubuntu-17.10

00:09:50

passed #12212
ubuntu-18.04

00:09:20