Take a GError * for typelib loading code, validate the header. This
fixes bizarre errors from gjs where g_irepository_require would happily
load old typelibs.
Split out GIBaseInfo to a separate source file.
Move out definitions to gibaseinfo.h/gitypelib.h/gitypes.h
and girepository-private.h
Install gibaseinfo.h/gitypelib.h and gitypes.h as well, but
require users to include girepository.h