Make stat() work on device files again.

FileDescriptor will now keep a pointer to the original inode even after
opening it resolves to a character device.

Fixed up /bin/ls to display major and minor device numbers instead of size
for device files.

Kernel/FileDescriptor.h

@@ -6,6 +6,7 @@
 #include <AK/ByteBuffer.h>
 #include <AK/CircularQueue.h>
 #include <AK/Retainable.h>
+#include <AK/Badge.h>
 
 class TTY;
 class MasterPTY;
@@ -68,6 +69,8 @@ public:
 
     ByteBuffer& generator_cache() { return m_generator_cache; }
 
+    void set_original_inode(Badge<VFS>, RetainPtr<Inode>&& inode) { m_inode = move(inode); }
+
 private:
     friend class VFS;
     explicit FileDescriptor(RetainPtr<Inode>&&);