[tools] Allow struct types in definitions

Allow struct type names in definitions, which result in struct buffer
pointers in generated code.

scripts/definitions/types/__init__.py

@@ -24,3 +24,4 @@ from .function import Function, Method, Param
 from .type import Type
 from .primitive import get_primitive
 from .objref import ObjectRef
+from .struct import Struct

scripts/definitions/types/struct.py

@@ -0,0 +1,17 @@
+from .type import Type
+
+class Struct(Type):
+    def __repr__(self):
+        return f'Struct({self.name})'
+
+    def c_names(self, options):
+        one = f"struct j6_{self.name} *"
+        two = "size_t"
+
+        out = bool({"out", "inout"}.intersection(options))
+        if out:
+            two += " *"
+        return ((one, ""), (two, "_size"))
+
+    def cxx_names(self, options):
+        return self.c_names(options)