Make meson link libmutter using -fvisibility=hidden, and introduce META_EXPORT
and META_EXPORT_TEST defines to mark a symbols as visible.
The TEST version is meant to be used to flag symbols that are only used
internally by mutter tests, but that should not be considered public API.
This allows us to be more precise in selecting what is exported and what is
not, without the need of a version-script file that would be more complicated
to maintain.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/395
Some types were declared in the public headers so that g-ir-scanner
could resolve the types. This caused warnings when using
-Wredundant-decls, so only redeclare them for the gir scanner.
This is a GAppLaunchContext subclass meant to replace usage of
GdkAppLaunchContext in gnome-shell.
Launch contexts get created from the MetaStartupNotification as
they are closely related. The messaging underneath depends on
the availability of a X11 display, if there is one we go through
it (and libsn). If there is none, we still create startup sequences
manually for wayland clients.
