The gtk bookmarks file is now in XDG dir, so let's first try there and
otherwise fall back to the old location

taken from:
https://git.gnome.org/browse/gedit/commit/?id=f0454abbec92f34431bd59fd1e3da6ad346a000e

GIO commit for reference:
https://git.gnome.org/browse/glib/commit/?id=510ba9b4efe1813e24c6dfa7405c3547bf9efdd7

ported from:
https://git.gnome.org/browse/gedit/commit/?id=b8b6fe708eddd6a9d471ecd04c38e790d8c0bc7c

old issue, also present in 1.16

fix taken from:
https://git.gnome.org/browse/gedit/commit/?id=bc5d893229e62c85f6956c17a8471cb5fdab10ea

mostly adapted from:
https://git.gnome.org/browse/gedit/commit/?id=3f5c69427579f80e8614f551aafa89baa9bfd0ca
https://git.gnome.org/browse/gedit/commit/?id=a2c9247c5fecea8d03917e7b0fa93447820439d2
https://git.gnome.org/browse/gedit/commit/?id=ccd39a71eab7fe04ea52cb10bd2282c95d8374c3
https://git.gnome.org/browse/gedit/commit/?id=2dbe5e048766a94b2ba42346b5d197edc92cd03d
https://git.gnome.org/browse/gedit/commit/?id=b3f6fd5c7ab9e433dd7698a25d9dc00867c04ad9
https://git.gnome.org/browse/gedit/commit/?id=2273ba27e85588c10788039b66b083aba6b50660
https://git.gnome.org/browse/gedit/commit/?id=48d33cf9dd29d8a6d42e60e3254c883f1f9ffb56
https://git.gnome.org/browse/gedit/commit/?id=7f37ff4fa2c9dd8f42ff527f4e1d0a148c39eb0e
https://git.gnome.org/browse/gedit/commit/?id=0d36d6e09a58210c365264c591fafb5d0b3d9323
https://git.gnome.org/browse/gedit/commit/?id=ac4f2048d6af5b2dbfc7ff6448bc51f3e2b324b6
https://git.gnome.org/browse/gedit/commit/?id=5540838a7dff1d025b995c251f51c1c29ce0c0ce
https://git.gnome.org/browse/gedit/commit/?id=d48cd10bf0bb99ead7b1af1ead52f1e554ad239d
https://git.gnome.org/browse/gedit/commit/?id=5169aa5cd4b1d95fb869df7c0b24c886cb33a1aa

registering on message bus won't work with introspection
due to varargs functions used in message bus code

we don't need a build breakage on the first deprecated item, thanks