g_dbus_address_escape_value: add

This is a GLib reimplementation of dbus_address_escape_value().
It's useful if you want to construct a D-Bus address from pieces:
for instance, if you have a listening Unix socket whose path is known,
and you want to connect a D-Bus peer to it.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=693673


Reviewed-by: Colin Walters <walters@verbum.org>
[amended to add Since: 2.36 as per review]
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>