Kernel: Some futex improvements

This adds support for FUTEX_WAKE_OP, FUTEX_WAIT_BITSET, FUTEX_WAKE_BITSET,
FUTEX_REQUEUE, and FUTEX_CMP_REQUEUE, as well well as global and private
futex and absolute/relative timeouts against the appropriate clock. This
also changes the implementation so that kernel resources are only used when
a thread is blocked on a futex.

Global futexes are implemented as offsets in VMObjects, so that different
processes can share a futex against the same VMObject despite potentially
being mapped at different virtual addresses.

Kernel/VM/Region.h

@@ -192,6 +192,11 @@ public:
         return m_offset_in_vmobject;
     }
 
+    size_t offset_in_vmobject_from_vaddr(VirtualAddress vaddr) const
+    {
+        return m_offset_in_vmobject + vaddr.get() - this->vaddr().get();
+    }
+
     size_t amount_resident() const;
     size_t amount_shared() const;
     size_t amount_dirty() const;