[OE-core] GStreamer recipes migration to Meson and _git.bb recipes?

[Philippe Normand]

Hi folks,

It would be convenient to have _git.bb GStreamer recipes, for
development purposes. There were some in the past but they were not
very well maintained and they had outdated SRCREVs. Would it be
acceptable to include _git.bb recipes relying on ${AUTOREV} in the
tree?

We also plan to migrate the recipes to Meson, especially because the
autotools build will be removed from GStreamer upstream, most probably
before the 1.18 stable release.

Philippe