Add scrollpanel widget

This PR introduces a new ScrollPanel component with the following
capabilities:
- Scroll Orientation Support: Allows scrolling in horizontal, vertical,
  or both directions, providing flexibility for different use cases.
- Partial Object Rendering: Supports partial rendering of objects that
  are only partially visible within the scroll boundaries, improving
  visual accuracy and performance.
- Boundary-Constrained Mouse Interaction: Handles mouse events strictly
  within the panel's visible boundaries, preventing interaction with
  objects outside the scrollable area.
- Minimum Internal Size (min_width, min_height): Introduces support for
  virtual space management, allowing the panel to maintain a minimum
  internal size independent of its actual on-screen dimensions. Even
  when the panel is resized, this ensures that the content respects a
  defined virtual space (with min_width and min_height), effectively
  simulating a larger internal canvas. This is particularly useful for
  large content or scenarios where a more extensive scrollable area is
  required than the current visible panel.

source/gui/GUIStringConversions.cpp

@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2024 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -18,6 +18,7 @@
 #include "precompiled.h"
 
 #include "gui/CGUI.h"
+#include "gui/SettingTypes/EScrollOrientation.h"
 #include "gui/SettingTypes/CGUIString.h"
 #include "ps/CLogger.h"
 
@@ -244,3 +245,18 @@ bool CGUI::ParseString<CGUIList>(const CGUI* UNUSED(pGUI), const CStrW& UNUSED(V
 {
 	return false;
 }
+
+template <>
+bool CGUI::ParseString<EScrollOrientation>(const CGUI* UNUSED(pGUI), const CStrW& Value, EScrollOrientation& Output)
+{
+	if (Value == L"vertical")
+		Output = EScrollOrientation::VERTICAL;
+	else if (Value == L"horizontal")
+		Output = EScrollOrientation::HORIZONTAL;
+	else if (Value == L"both")
+		Output = EScrollOrientation::BOTH;
+	else
+		return false;
+
+	return true;
+}