[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.

src/kernel/objects/thread.cpp

@@ -1,5 +1,6 @@
 #include <util/pointers.h>
 
+#include "capabilities.h"
 #include "cpu.h"
 #include "logger.h"
 #include "memory.h"
@@ -31,7 +32,8 @@ thread::thread(process &parent, uint8_t pri, uintptr_t rsp0) :
         m_tcb.rsp0 = rsp0;
 
     m_creator = current_cpu().thread;
-    m_self_handle = parent.add_handle(this, thread::parent_caps);
+    m_self_handle = g_cap_table.create(this, thread::parent_caps);
+    parent.add_handle(m_self_handle);
 }
 
 thread::~thread()