GTrashStack: uninline and deprecate

Deprecate GTrashStack and remove the inline implementations for the
functions.  This will help us clean up the mess that is inline functions
in GLib.

Because of how G_INLINE_FUNC worked, we have these functions on our ABI,
so we must continue to export them as normal functions.  We are safe to
remove the inline versions, however, because any existing binaries will
continue to carry them and any new builds will just start using the
non-inline versions.

https://bugzilla.gnome.org/show_bug.cgi?id=757374