Kernel: Note if the page fault address is a destroyed smart pointer

While I was working on LibWeb, I got a page fault at 0xe0e0e0e4.
This indicates a destroyed RefPtr if compiled with SANITIZE_PTRS
defined. However, the page fault handler didn't print out this
indication.

This makes the page fault handler print out a note if the faulting
address looks like a recently destroyed RefPtr, OwnPtr, NonnullRefPtr,
NonnullOwnPtr, ThreadSafeRefPtr or ThreadSafeNonnullRefPtr. It will
only do this if SANITIZE_PTRS is defined, as smart pointers don't get
scrubbed without it being defined.

AK/NonnullRefPtr.h

@@ -6,6 +6,8 @@
 
 #pragma once
 
+#define NONNULLREFPTR_SCRUB_BYTE 0xe1
+
 #ifdef KERNEL
 #    include <Kernel/Library/ThreadSafeNonnullRefPtr.h>
 #else
@@ -97,7 +99,7 @@ public:
         unref_if_not_null(m_ptr);
         m_ptr = nullptr;
 #    ifdef SANITIZE_PTRS
-        m_ptr = reinterpret_cast<T*>(explode_byte(0xb0));
+        m_ptr = reinterpret_cast<T*>(explode_byte(NONNULLREFPTR_SCRUB_BYTE));
 #    endif
     }