Most of the code for handling stack-allocated infos was correct, it was
just missing code to initialise the `GTypeInstance` member.
Since `GTypeInstance` isn’t really designed for stack allocation, this
is a little hacky — it requires setting up the member within
`GTypeInstance` manually. It works, though.
The externally visible consequence of this, though, is that
stack-allocated `GIBaseInfo`s now need to be cleared when they’re
finished being used. This allows the `GTypeClass` ref to be dropped.
All users of the stack-allocated APIs in libgirepository will need to
adapt to this change.
Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Fixes: #3218
bf4cf2d464