Focus: Reworking FocusWindow() so in Docking branch we can fix CTRL+Tab being out of order on Docked windows because WindowsFocusOreder is poorly maintained.

When merging this and d9bca0d8 in Docking we'll replace two ocurrences of RootWindow with RootWindowDockStop.

imgui.cpp

@@ -6040,17 +6040,18 @@ void ImGui::FocusWindow(ImGuiWindow* window)
 
     // Move the root window to the top of the pile
     IM_ASSERT(window->RootWindow != NULL);
-    window = window->RootWindow;
+    ImGuiWindow* focus_front_window = window->RootWindow; // NB: In docking branch this is window->RootWindowDockStop
+    ImGuiWindow* display_front_window = window->RootWindow;
 
     // Steal focus on active widgets
-    if (window->Flags & ImGuiWindowFlags_Popup) // FIXME: This statement should be unnecessary. Need further testing before removing it..
-        if (g.ActiveId != 0 && g.ActiveIdWindow && g.ActiveIdWindow->RootWindow != window)
+    if (focus_front_window->Flags & ImGuiWindowFlags_Popup) // FIXME: This statement may be unnecessary? Need further testing before removing it..
+        if (g.ActiveId != 0 && g.ActiveIdWindow && g.ActiveIdWindow->RootWindow != focus_front_window)
             ClearActiveID();
 
     // Bring to front
-    BringWindowToFocusFront(window);
-    if (!(window->Flags & ImGuiWindowFlags_NoBringToFrontOnFocus))
-        BringWindowToDisplayFront(window);
+    BringWindowToFocusFront(focus_front_window);
+    if ((display_front_window->Flags & ImGuiWindowFlags_NoBringToFrontOnFocus) == 0)
+        BringWindowToDisplayFront(display_front_window);
 }
 
 void ImGui::FocusTopMostWindowUnderOne(ImGuiWindow* under_this_window, ImGuiWindow* ignore_window)