ci: Build with -Dothers=enabled

See merge request !167

since it's off by default.  Add ${LOADERS_FLAGS} to the macOS and asan
runs for the same reason.

Also add -Dgif=enabled for consistency.

build: Avoid unnecessary format() when building long options

See merge request !166

fix build failure due to typo in the build script

See merge request !165

When building a custom_target command line,

    '--opt=@0@'.format(x.full_path())

can be replaced with

    '--opt', x

which is simpler and avoids hiding the `x` dependency from Meson.  In some
cases we were declaring that dependency explicitly; stop doing so.

This should fix an occasional build error from build-aux/gen-resources.py
when glib is built as a parallel subproject:

    FileNotFoundError: [Errno 2] No such file or directory: '[...]/glib-2.80.0/gio/glib-compile-resources'

We can't just add glib_compile_resources to `depends` because `depends`
doesn't accept `external_program` arguments.

The fixed commit had a typo where it would try to call a nonexistant
function instead of the .contains method of the relevant array.
This was only made visible when the "other" loaders were enabled so it
is triggered all the time.

This was made visible when working on
https://gitlab.archlinux.org/archlinux/packaging/packages/gdk-pixbuf2/-/merge_requests/1

Fixes: 81a77399

 ("Update the testsuite")
Signed-off-by: Christian Heusel <christian@heusel.eu>

This was found in the asan build in ci.

build: Disable fringe loaders by default

See merge request !163

Skip tests when necessary because we don't built the required
loaders.

Add 'gif' and 'others' options for the gif loader and all the
other remaining loaders. This makes it easier for distros to
ship a sane subset of loaders.

Update gi-docgen's wrap

See merge request !151

Meson will check the dependency based on the subproject's overrides.

Use the `provide` override to ensure that Meson knows what the gi-docgen
wrap provides.

Fix some GIR annotations

See merge request !146

meson: Override dependencies to improve usage as a subproject

See merge request !148

With this change, gdk-pixbuf can be consumed as a subproject without
making any changes to the build files of a project. All you need to do
is provide a wrap file with a `[provide]` section:

https://mesonbuild.com/Wrap-dependency-system-manual.html#provide-section

This is also necessary because otherwise projects need to hard-code
the subproject name, which might be `gdk-pixbuf` when using `wrap-git`
or `gdk-pixbuf-2.42.10` when using `wrap-file` (to build from
a release tarball). This can cause conflicts between different
subprojects that consume gdk-pixbuf differently.

Other projects like glib, cairo, pango, etc already do this.

jpeg: Bump up the memory limit to 1GB

Closes #218

See merge request !147

Let's play some more whack-a-mole.

Fixes: #218

docs: Also search for rst2man.py

See merge request !145

ci: Bump up Meson on macOS

See merge request !140

jpeg: Increase memory limit for loading image data

Closes #216

See merge request !143