Allow stack allocating GIBaseInfo, add stack retrieval variants

We don't want to malloc each GIBaseInfo when they can be used in
function invocation; instead, allow stack allocation.

There were a lot of structure typedefs which were actually just
exactly the same as GIBaseInfo, with the one exception of GITypeInfo.

Instead, just put the single GITypeInfo boolean inside GIBaseInfo
as a bit in a bitfield.

GIBaseInfo is still opaque publicly; GIRealInfo is the new
internal structure.

Using this, add new functions to retrieve arguments and argument types
on the stack.

https://bugzilla.gnome.org/show_bug.cgi?id=604074