There are a handful of APIs in libgirepository which are used on
performance-sensitive code paths in language bindings (such as looking
at arguments when doing function calls). Historically libgirepository
has provided a stack-allocated variant for them, which avoids returning
a newly allocated `GIBaseInfo`. Since moving to glib.git and porting to
`GTypeInstance`, that stack allocated version has been broken.
This commit fixes it, by exposing obfuscated stack allocatable versions
of `GITypeInfo` and `GIArgInfo`, which are the two `GIBaseInfo`
subtypes which can be returned by the stack allocation functions.
The commit includes unit tests for them.
Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Fixes: #3217
2a99d4b168