uobject: Make the relevant UPkg available to objects.

uobject: Make the relevant UPkg available to objects.

Instead of passing around raw "struct upkg" pointers, keep the
GTypeModule implementation around instead (which contains this
information).  This allows access to all package functions; in
particular, it allows access to the package name.

Modify implementations to get the raw "struct upkg" from the upkg_file
reference instead.