Keeping all dependencies inside the main manifest is very annoying
because flatpak-builder will check them every time the package is
rebuilt. Worse, sometimes the cache won't be hit (even though it should
have), resulting into a rebuild of many dependencies. I create a BaseApp
build which is the recommended process (and not creating our own runtime
based on GNOME one's, as I first thought) which won't need to be built
as often as the main manifests. The other advantage is obviously that
this BaseApp can be shared between the dev and nightly (and likely even
the stable later) builds. I will only keep differences inside the main
manifests (for instance lcms2 which requires a higher version on master
than on the GNOME runtime and the last dev release).
I also move webkitgtk as the first dependencies since it takes too long
and flatpak uses a sequential dependency graph (so any change to a
previously listed dependency, even when actually unrelated, was
triggering a rebuild of webkitgtk!).
Only remaining issue is that I don't manage yet to run the cleanup of
the BaseApp at the end of the main manifests (for files needed for
building, but not at runtime).