flatpak: Build folks with meson

Folks recently gained support for the Meson build system, so use that
instead of autotools. This should make the build faster and more
future-proof (since the autotools build might not survive for long).
5 jobs for <span class="ref-name">wip/nielsdg/folks-meson</span> in 26 minutes and 42 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #275310
fedora

00:10:10

passed #275311
ubuntu

00:12:11

 
  Test
passed #275312
flatpak

00:10:58

 
  Deploy
passed #275313
review

00:02:03

passed #275314
allowed to fail manual
stop_review

00:01:28