[zion] Dynamically check Capability type.

Instead of passing an enum with the capability when creating it, relying
on polymorphism and a template struct tag to determine the object type
at runtime.

This is cleaner and avoids errors where we pass the wrong capability
type with the cap and do a bad cast at runtime.

zion/object/kernel_object.h

@@ -2,4 +2,22 @@
 
 #include "lib/ref_counted.h"
 
-class KernelObject : public RefCounted<KernelObject> {};
+class KernelObject : public RefCounted<KernelObject> {
+ public:
+  enum ObjectType {
+    INVALID = 0x0,
+    PROCESS = 0x1,
+    THREAD = 0x2,
+    ADDRESS_SPACE = 0x3,
+    MEMORY_OBJECT = 0x4,
+    CHANNEL = 0x5,
+    PORT = 0x6,
+  };
+
+  virtual uint64_t TypeTag() = 0;
+};
+
+template <typename T>
+struct KernelObjectTag {
+  static const int type = KernelObject::INVALID;
+};