The identifier doesn't have any properties of a variable and we only
use it for holding the name before it is freed.

Use get_type instead of get_typev in the type_new_* functions and get
rid of get_typev.

Use pointers for the information for structures, enumerations,
functions and interfaces so that we can determine whether or not the
type has been defined yet and to enable more information to be stored.

widl: Hide the details of where arguments, fields, values and cases are stored in the type_t structure for functions, structures, enums and unions.

widl: Follow aliases in check_remoting_fields so that the fields for the type are correctly enumerated.

oleidl.h isn't usable without winuser.h being included first due to
using the LPMSG type, so explicitly include it by adding a cpp_quote
statement to oleidl.idl. In the PSDK it is implicitly included as
IDL-generated header includes windows.h, which in turn includes
winuser.h.