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.
Generating gir and typelib files has inter-dependencies that may depend
on other elements.
For example, glib requires gobject and gdump generated files require
gmodule, so we've a cyclic dependency because gmodule requires gobject,
that requires glib.
To prevent this, let's just generate the introspection files at once in
a different meson file so that we don't have to deal with this.
As per this we could even revert commit fa37ab6d0 since gio is now
compiled before the gir files.
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
