Further reduce circular dependencies

[smcv]

Continuation of #5409, #5801. Any prefix of this branch should be OK to apply, so it can be broken into smaller pieces if reviewers would prefer that.

The overall goal of this branch is to break up unmanageably large translation units, and make the common/ code more understandable by separating it into layers (utils < exports < context, utils < xml-utils < repo-utils < dir, etc.) instead of having all modules call into all other modules.

My ulterior motive for this refactoring is that my day job involves maintaining Steam's pressure-vessel tool, which reuses some of the lower-level parts of Flatpak (notably -utils, -exports and some of -run) but not the higher-level parts (in particular anything with libostree in it). At the moment we do that with a lot of #if 0 around the parts we don't want, but if I could copy the lower-level translation units in their entirety while leaving out the ones that would add dependencies, that would be a lot easier!

But, even without that factor, I think this PR is an improvement to Flatpak - having it be layered rather than entangled makes it easier for contributors and maintainers to understand the overall system.

Having that layering should also allow us to drop some of the library dependencies from Flatpak's own ancillary tools: for example, there's no real reason why the portal and the system helper should need dependencies on libostree, libsoup/libcurl or libarchive, but at the moment they have to link libflatpak_common_dep which depends on those.

I think the version in this PR achieves reasonably good layering, especially in the lower layers, for example:

• libglnx < glib-backports < everything else
• metadata < everything
• errors < utils < almost everything else
• utils < appdata
• utils < bwrap < exports < context < run
• utils < instance
• utils < ref-utils < repo-utils < bundle-ref
• utils < ref-utils < repo-utils < {dir, dir-utils} < installation
• ... < {dir, dir-utils} < installed-ref
• ... < {dir, dir-utils} < oci-registry
• ... < {dir, dir-utils} < related-ref
• ... < {dir, dir-utils} < remote

Limitations:

• The higher-level "package management" modules auth, dir and dir-utils are currently still entangled. My knowledge of the "package manager" layer of Flatpak is limited, so I'd prefer it if someone who is better at the conceptual design of Flatpak can disentangle that part.
• -run and -dir are also still entangled, because -run calls flatpak_deploy_data_get_commit(), while -dir calls flatpak_run_get_minimal_env() among others. This PR is already large, so I'd prefer to disentangle that another time!

---

Commits

• utils: Include flatpak-metadata-private.h instead of -run-private.h

  This avoids a circular dependency between -run and -utils.

• common: Move OCI registry manipulation into FlatpakOciRegistry

  This is a step towards making flatpak-utils conceptually "smaller"
  than all other translation units, with no dependencies beyond GLib and
  libglnx. In particular, consolidating all the OCI registry manipulation
  into one place means we can build other translation units without
  libarchive.

  This would also be a step towards being able to provide a build-time
  option to build a libostree-only version of Flatpak without the OCI
  feature or the direct libarchive dependency, if someone wanted to
  implement that.

• repo-utils: New header for some implementation details of a repository

  This will reduce circular dependencies involving FlatpakDir.

• common: Break out the parts of flatpak-utils that deal with FlatpakDir

  This breaks the circular dependency between flatpak-utils and flatpak-dir.
  There is still a circular dependency between flatpak-dir and
  flatpak-dir-utils, but I don't want to make flatpak-dir even larger.

• common: Explicitly include ostree.h where needed

  A subsequent commit will remove it from flatpak-utils-private.h.

• utils: Move OstreeRepo configuration accessors to a new translation unit

  This is a step towards removing the libostree dependency from
  flatpak-utils, which should be one of the lowest-level components.

• ref-utils: Move flatpak_get_arch_for_ref() to here

  The declaration was already in flatpak-ref-utils-private.h.

  Fixes: 5dae1fc "Break out ref helper functions to separate file"

• dir: Move some more implementation details into repo-utils

  This allows repo-utils to be kept lower-level than dir.

• utils: Move more repository functionality into repo-utils

• utils: Move more summary parsing into repo-utils

• utils: Export flatpak_get_compat_arch()

  This will allow its caller to be moved into repo-utils.

• utils: Move more repository functionality to repo-utils

  This further reduces circular dependencies: utils no longer has a
  circular dependency with repo-utils or xml-utils.

• utils: Move remaining direct ostree dependencies to repo-utils

• utils: Remove unnecessary flatpak-ref-utils-private.h inclusion

  Include flatpak-ref-utils-private.h explicitly in each remaining
  module that needs it (mostly for FlatpakDecomposed).

• prune: Include flatpak-variant-private.h before its -impl-private.h

  This ensures that declarations are visible.

• utils: Remove flatpak-variant-private.h, no longer necessary

[smcv]

@TingPing, if you liked #5801 then this might also be of interest.

[GeorgesStavracas]

Looks good to me, only one small comment about translation files, should be easy to address

[GeorgesStavracas]

I think you need to add this file to POTFILES.in