monitor: add object-add (QMP) and object_add (HMP) command

Add two commands that are the monitor counterparts of -object.  The commands
have the same Visitor-based implementation, but use different kinds of
visitors so that the HMP command has a DWIM string-based syntax, while
the QMP variant accepts a stricter JSON-based properties dictionary.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

include/qapi/visitor.h

@@ -13,6 +13,7 @@
 #ifndef QAPI_VISITOR_CORE_H
 #define QAPI_VISITOR_CORE_H
 
+#include "qemu/typedefs.h"
 #include "qapi/qmp/qobject.h"
 #include "qapi/error.h"
 #include <stdlib.h>
@@ -26,8 +27,6 @@ typedef struct GenericList
     struct GenericList *next;
 } GenericList;
 
-typedef struct Visitor Visitor;
-
 void visit_start_handle(Visitor *v, void **obj, const char *kind,
                         const char *name, Error **errp);
 void visit_end_handle(Visitor *v, Error **errp);