[kernel] Make capabilities/handles global

Instead of handles / capabilities having numeric ids that are only valid
for the owning process, they are now global in a system capabilities
table. This will allow for specifying capabilities in IPC that doesn't
need to be kernel-controlled.

Processes will still need to be granted access to given capabilities,
but that can become a simpler system call than the current method of
sending them through mailbox messages (and worse, having to translate
every one into a new capability like was the case before). In order to
track which handles a process has access to, a new node_set based on
node_map allows for an efficient storage and lookup of handles.

definitions/syscalls.def

@@ -32,7 +32,7 @@ interface syscalls [syscall] {
     # supplied list is not big enough, will set the size
     # needed in `size` and return j6_err_insufficient
     function handle_list {
-        param handles ref object [list inout zero_ok] # A list of handles to be filled
+        param handles struct handle_descriptor [list inout zero_ok] # A list of handles to be filled
     }
 
     # Create a clone of an existing handle, possibly with