In de26d148, we added support
for the `--introspection-dump` CLI flag inside GApplication
but that initialized a bunch of classes that e.g. try to migrate config files.
Let’s move it to the beginning of the main program entry point before
GApplication is even created to avoid having to set `HOME` in the Nix package
(introduced in 15f61da9)
and prevent warnings about data files not being installed.

We were not actually writing the values anywhere.

Also use project-specific env vars, which require Meson 0.58.0:
https://mesonbuild.com/Release-notes-for-0-58-0.html#mesonadd_dist_script-allowed-in-subprojects

This is not a library so it is not really useful for external consumers but it is still nice to have as a development reference.

It is required for Tartan to properly analyze our types.
Also will be required for API docs.

Otherwise starting the app might fail when the XDG directories do not exist yet (e.g. in fresh build sandbox on CI).

WARNING: Project targeting '>= 0.57.0' but tried to use feature deprecated since '0.56.0': meson.source_root. use meson.current_source_dir instead.
WARNING: Project targeting '>= 0.57.0' but tried to use feature deprecated since '0.55.0': ExternalProgram.path. use ExternalProgram.full_path() instead

find_program is the correct function.

DEPRECATION: i18n.merge_file does not take any positional arguments. This will become a hard error in the next Meson release.

BuohWindow is GtkApplicationWindow so we should just pass GApplication to the constructor.

Also do some related clean-ups.

https://www.bassi.io/articles/2021/07/27/final-types/

Requires GLib 2.70

When the image changes, the pixbuf does too so it does not make much sense to cache the pixbuf.
Unless it has something to do with zoom but then the cache is probably the wrong layer.

They are now pinned by default even for shell.
We also started using Niv for easier updating –
one can just run `nix-shell --run 'niv update'`
instead of manually replacing the commit id.

It is deprecated: https://discourse.gnome.org/t/port-your-module-from-g-memdup-to-g-memdup2-now/5538

The build complained

    'gdk_cursor_new' is deprecated: Use 'gdk_cursor_new_for_display' instead

Unfortunately, the API changes in GTK 4.