Make classes not depend on the implicit GImGui context (#5856, #6199): ImGuiWindow, ImGuiInputTextCallbackData, ImGuiListClipper, ImGuiStackSizes

This commit is a preparation toward adding ImGui apis with explicit context
and making ImGui applications being able to use multiple context at the same time
whatever their concurrency model.

This commit modifies ImGuiInputTextCallback, ImGuiListClipper and ImGuiStackSize so those classes do not to depend on GImGui context anymore.

About ImGuiInputTextCallback:
- ImGuiInputTextCallback depends on ImGuiContext because it has a
  `InsertChars` method adding character to `g.InputTextState`
- To make ImGuiInputTextCallback aware of which context to use, the
  appropriate context is given as argument of ImGuiInputTextCallback
  constructor.

About ImGuiListClipper:
- ImGuiListClipper apply to a context through its `Begin`, `End`, and `Step`
  method.
- To make ImGuiListClipper aware of which context to use, the
  appropriate context is given as argument of ImGuiListClipper
  constructor.
- Since the behavior is different than previously the class has been
  renamed ImGuiListClipperEx
- In order to preserve backward compatibility, a subclass of ImGuiListClipperEx
  named ImGuiListClipper has been defined and forward the implicit context
  to ImGuiListClipperEx parent.

About ImGuiTextFilter:
- ImGuiTextFilter depends on the implicit context because the Draw(..)
  method call ImGui::InputText(...)
- Instead from that commit the Draw(...) method takes an explicit context
  as first argument
- Since the behavior is different than previously the class has been
  renamed ImGuiTextFilterEx
- In order to preserve backward compatibility, a subclass of ImGuiTextFilterEx
  named ImGuiTextFilter has been defined. This subclass has a draw method
  override which and forward the implicit context to the parent class Draw(...)

About ImGuiStackSizes:
- ImGuiStackSizes was depending on ImGuiContext because of its
  `SetToCurrentState` and `CompareWithCurrentState` method
- ImGuiStackSizes is an helper object use
  for comparing state of context. It does not necessarily need to
  compare the same context. For that reason, as opposed to previous
  classes it takes the context it wants to compare to as argument of
  its method.
- For this occasion `SetToCurrentState` and `CompareWithCurrentState`
  have been renamed `SetToContextState` and `CompareWithContextState`
  to match the new method signature.

ImGuiListClipper

ImGuiInputTextCallbackData

imgui_internal.h

@@ -1182,8 +1182,8 @@ struct IMGUI_API ImGuiStackSizes
     short   SizeOfDisabledStack;
 
     ImGuiStackSizes() { memset(this, 0, sizeof(*this)); }
-    void SetToCurrentState();
-    void CompareWithCurrentState();
+    void SetToContextState(ImGuiContext* ctx);
+    void CompareWithContextState(ImGuiContext* ctx);
 };
 
 // Data saved for each window pushed into the stack
@@ -2237,6 +2237,7 @@ struct IMGUI_API ImGuiWindowTempData
 // Storage for one window
 struct IMGUI_API ImGuiWindow
 {
+    ImGuiContext*           Ctx;                                // Parent UI context (needs to be set explicitly by parent).
     char*                   Name;                               // Window name, owned by the window.
     ImGuiID                 ID;                                 // == ImHashStr(Name)
     ImGuiWindowFlags        Flags;                              // See enum ImGuiWindowFlags_
@@ -2347,10 +2348,10 @@ public:
 
     // We don't use g.FontSize because the window may be != g.CurrentWindow.
     ImRect      Rect() const            { return ImRect(Pos.x, Pos.y, Pos.x + Size.x, Pos.y + Size.y); }
-    float       CalcFontSize() const    { ImGuiContext& g = *GImGui; float scale = g.FontBaseSize * FontWindowScale; if (ParentWindow) scale *= ParentWindow->FontWindowScale; return scale; }
-    float       TitleBarHeight() const  { ImGuiContext& g = *GImGui; return (Flags & ImGuiWindowFlags_NoTitleBar) ? 0.0f : CalcFontSize() + g.Style.FramePadding.y * 2.0f; }
+    float       CalcFontSize() const    { ImGuiContext& g = *Ctx; float scale = g.FontBaseSize * FontWindowScale; if (ParentWindow) scale *= ParentWindow->FontWindowScale; return scale; }
+    float       TitleBarHeight() const  { ImGuiContext& g = *Ctx; return (Flags & ImGuiWindowFlags_NoTitleBar) ? 0.0f : CalcFontSize() + g.Style.FramePadding.y * 2.0f; }
     ImRect      TitleBarRect() const    { return ImRect(Pos, ImVec2(Pos.x + SizeFull.x, Pos.y + TitleBarHeight())); }
-    float       MenuBarHeight() const   { ImGuiContext& g = *GImGui; return (Flags & ImGuiWindowFlags_MenuBar) ? DC.MenuBarOffset.y + CalcFontSize() + g.Style.FramePadding.y * 2.0f : 0.0f; }
+    float       MenuBarHeight() const   { ImGuiContext& g = *Ctx; return (Flags & ImGuiWindowFlags_MenuBar) ? DC.MenuBarOffset.y + CalcFontSize() + g.Style.FramePadding.y * 2.0f : 0.0f; }
     ImRect      MenuBarRect() const     { float y1 = Pos.y + TitleBarHeight(); return ImRect(Pos.x, y1, Pos.x + SizeFull.x, y1 + MenuBarHeight()); }
 };