We used to store the search paths into a GSList but this is not
efficient for various reasons, so replace this with an array so that we
can replace return just a GStrv in the public API.
For the moment, this is enough to roughly verify that the port to
`GTypeInstance` has not massively broken things. It’s not anywhere near
sufficient to qualify as a proper test suite though.
Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Helps: #3155