AK: Rename the common integer typedefs to make it obvious what they are.

These types can be picked up by including <AK/Types.h>:

* u8, u16, u32, u64 (unsigned)
* i8, i16, i32, i64 (signed)

Kernel/FileSystem/VirtualFileSystem.h

@@ -107,7 +107,7 @@ private:
 
     RefPtr<Inode> m_root_inode;
     Vector<OwnPtr<Mount>> m_mounts;
-    HashMap<dword, Device*> m_devices;
+    HashMap<u32, Device*> m_devices;
 
     RefPtr<Custody> m_root_custody;
 };