When doing type resolution on a string, treat it as its own ctype

When doing type resolution on a string, treat it as its own ctype

Calling _resolve_param_type on a string instead of Node is fairly unusual,
and (as far as I could see) basically only happened in the Array processing
code.  We were passing None as the ctype in this case, but we might as well
try using the name as a ctype too.

This fixes using GCallback (and in general any item in an array that comes
from an included gir).