[kernel] Add userspace threading

Implement the syscalls necessary for threads to create other threads in
their same process. This involved rearranging a number of syscalls, as
well as implementing object_wait and a basic implementation of a
process' list of handles.

src/kernel/objects/kobject.h

@@ -41,6 +41,9 @@ public:
 	/// \returns   The object type for the koid
 	static type koid_type(j6_koid_t koid);
 
+	/// Get this object's type
+	inline type get_type() const { return koid_type(m_koid); }
+
 	/// Get this object's koid
 	inline j6_koid_t koid() const { return m_koid; }