LibCore: Introduce a C_OBJECT macro.

This macro goes at the top of every CObject-derived class like so:

class SomeClass : public CObject {
    C_OBJECT(SomeClass)
public:
    ...

At the moment, all it does is create an override for the class_name() getter
but in the future this will be used to automatically insert member functions
into these classes.

Servers/WindowServer/WSWindow.h

@@ -16,6 +16,7 @@ class WSMouseEvent;
 
 class WSWindow final : public CObject
     , public InlineLinkedListNode<WSWindow> {
+    C_OBJECT(WSWindow)
 public:
     WSWindow(WSClientConnection&, WSWindowType, int window_id, bool modal, bool resizable, bool fullscreen);
     WSWindow(CObject&, WSWindowType);