[kernel] Let objects inherit caps from superclasses

The main point of this change is to allow "global" capabilities defined
on the base object type. The example here is the clone capability on all
objects, which governs the ability to clone a handle.

Related changes in this commit:
- Renamed `kobject` to `object` as far as the syscall interface is
  concerned. `kobject` is the cname, but j6_cap_kobject_clone feels
  clunky.
- The above change made me realize that the "object <type>" syntax for
  specifying object references was also clunky, so now it's "ref <type>"
- Having to add `.object` on everywhere to access objects in
  interface.exposes or object.super was cumbersome, so those properties
  now return object types directly, instead of ObjectRef.
- syscall_verify.cpp.cog now generates code to check capabilities on
  handles if they're specified in the definition, even when not passing
  an object to the implementation function.

scripts/definitions/types/interface.py

@@ -18,7 +18,7 @@ class Interface:
         self.desc = desc
 
         self.functions = [c for c in children if isinstance(c, Function)]
-        self.exposes = [e.type for e in children if isinstance(e, Expose)]
+        self.__exposes = [e.type for e in children if isinstance(e, Expose)]
 
     def __str__(self):
         parts = [f"interface {self.name}: {self.uid}"]
@@ -35,8 +35,12 @@ class Interface:
         mm = [(i, None, self.functions[i]) for i in range(len(self.functions))]
 
         base = len(mm)
-        for o in [e.object for e in self.exposes]:
+        for o in self.exposes:
             mm.extend([(base + i, o, o.methods[i]) for i in range(len(o.methods))])
             base += len(o.methods)
 
         return mm
+
+    @property
+    def exposes(self):
+        return [ref.object for ref in self.__exposes]

scripts/definitions/types/object.py

@@ -7,11 +7,12 @@ class Object:
         self.uid = uid
         self.options = opts
         self.desc = desc
-        self.super = typename
         self.methods = children
         self.cname = cname or name
         self.caps = caps
 
+        self.__super = typename
+
         from . import ObjectRef
         self.__ref = ObjectRef(name)
 
@@ -25,3 +26,8 @@ class Object:
         return "\n".join(parts)
 
     reftype = property(lambda self: self.__ref)
+
+    @property
+    def super(self):
+        if self.__super is not None:
+            return self.__super.object