Remove virtual inheritance from the codebase, refs 6b51d71c85, e21ebb37f5 e326ebae46.

Remove workaround in 3d07327837 / D2136, the pointer from IGUIObject to
IGUITextOwner that avoided the dynamic_cast.
Have the GUIObject implementing class take responsibility of calling the
virtual methods in the base classes.
Leaves the code in a clean state that can serve as an example for new
GUI object classes, such as D1346, refs #4683.

Differential Revision: https://code.wildfiregames.com/D2325
Comments By: Vladislav on IRC 2019-07-30, 2019-08-22, 2019-09-20-23
Tested on: clang 8.0.1, Jenkins

This was SVN commit r23020.

source/gui/CButton.cpp

@@ -25,8 +25,8 @@
 
 CButton::CButton(CGUI& pGUI)
 	: IGUIObject(pGUI),
-	  IGUIButtonBehavior(pGUI),
-	  IGUITextOwner(pGUI),
+	  IGUIButtonBehavior(*static_cast<IGUIObject*>(this)),
+	  IGUITextOwner(*static_cast<IGUIObject*>(this)),
 	  m_BufferZone(),
 	  m_CellID(),
 	  m_Caption(),
@@ -72,9 +72,21 @@ void CButton::SetupText()
 	CalculateTextPosition(m_CachedActualSize, m_TextPos, m_GeneratedTexts[0]);
 }
 
+void CButton::ResetStates()
+{
+	IGUIObject::ResetStates();
+	IGUIButtonBehavior::ResetStates();
+}
+
+void CButton::UpdateCachedSize()
+{
+	IGUIObject::UpdateCachedSize();
+	IGUITextOwner::UpdateCachedSize();
+}
+
 void CButton::HandleMessage(SGUIMessage& Message)
 {
-	// Important
+	IGUIObject::HandleMessage(Message);
 	IGUIButtonBehavior::HandleMessage(Message);
 	IGUITextOwner::HandleMessage(Message);
 }