[kernel] Pass objects not handles to syscall impls

This commit contains a couple large, interdependent changes:

- In preparation for capability checking, the _syscall_verify_*
  functions now load most handles passed in, and verify that they exist
  and are of the correct type. Lists and out-handles are not converted
  to objects.
- Also in preparation for capability checking, the internal
  representation of handles has changed. j6_handle_t is now 32 bits, and
  a new j6_cap_t (also 32 bits) is added. Handles of a process are now a
  util::map<j6_handle_t, handle> where handle is a new struct containing
  the id, capabilities, and object pointer.
- The kernel object definition DSL gained a few changes to support auto
  generating the handle -> object conversion in the _syscall_verify_*
  functions, mostly knowing the object type, and an optional "cname"
  attribute on objects where their names differ from C++ code.
  (Specifically vma/vm_area)
- Kernel object code and other code under kernel/objects is now in a new
  obj:: namespace, because fuck you <cstdlib> for putting "system" in
  the global namespace. Why even have that header then?
- Kernel object types constructed with the construct_handle helper now
  have a creation_caps static member to declare what capabilities a
  newly created object's handle should have.

src/libraries/j6/include/j6/types.h

@@ -27,14 +27,13 @@ typedef uint64_t j6_tag_t;
 #define j6_tag_from_irq(x)    ((x) | j6_tag_irq_base)
 #define j6_tag_to_irq(x)      ((x) & ~j6_tag_irq_base)
 
-/// Handles are references and capabilities to other objects. The least
-/// significant 32 bits are an identifier, and the most significant 32
-/// bits are a bitmask of capabilities this handle has on that object.
-typedef uint64_t j6_handle_t;
+/// Handles are references and capabilities to other objects.
+typedef uint32_t j6_handle_t;
 
-#define j6_handle_rights_shift 4
-#define j6_handle_id_mask 0xffffffffull
-#define j6_handle_invalid 0xffffffffull
+#define j6_handle_invalid ((j6_handle_t)-1)
+
+/// Bitfield for storage of capabilities
+typedef uint32_t j6_cap_t;
 
 enum j6_object_type {
 #define OBJECT_TYPE( name, val ) j6_object_type_ ## name = val,