HackStudio: Introduce a Tool class with subs CursorTool and WidgetTool

These will be used to draw out new widgets on a FormWidget, or in the
case of CursorTool, to select and manipulate existing widgets.

DevTools/HackStudio/Tool.h

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <AK/Noncopyable.h>
+
+class FormEditorWidget;
+class GMouseEvent;
+
+class Tool {
+    AK_MAKE_NONCOPYABLE(Tool)
+    AK_MAKE_NONMOVABLE(Tool)
+public:
+    virtual ~Tool() {}
+
+    virtual void on_mousedown(GMouseEvent&) = 0;
+    virtual void on_mouseup(GMouseEvent&) = 0;
+    virtual void on_mousemove(GMouseEvent&) = 0;
+
+    virtual const char* class_name() const = 0;
+
+    virtual void attach() {}
+    virtual void detach() {}
+
+protected:
+    explicit Tool(FormEditorWidget& editor)
+        : m_editor(editor)
+    {
+    }
+
+    FormEditorWidget& m_editor;
+};