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/CInput.cpp

@@ -40,7 +40,7 @@ extern int g_yres;
 CInput::CInput(CGUI& pGUI)
 	:
 	IGUIObject(pGUI),
-	IGUIScrollBarOwner(pGUI),
+	IGUIScrollBarOwner(*static_cast<IGUIObject*>(this)),
 	m_iBufferPos(-1),
 	m_iBufferPos_Tail(-1),
 	m_SelectingText(),
@@ -842,9 +842,15 @@ InReaction CInput::ManuallyHandleHotkeyEvent(const SDL_Event_* ev)
 	return IN_PASS;
 }
 
+void CInput::ResetStates()
+{
+	IGUIObject::ResetStates();
+	IGUIScrollBarOwner::ResetStates();
+}
 
 void CInput::HandleMessage(SGUIMessage& Message)
 {
+	IGUIObject::HandleMessage(Message);
 	IGUIScrollBarOwner::HandleMessage(Message);
 
 	switch (Message.type)