Nav: fixed c licking window decorations (e.g. resize borders) from losing focused item when within a child window using ImGuiChildFlags_NavFlattened.

In essence, using ImGuiFocusRequestFlags_RestoreFocusedChild here is a way to reduce changes caused by FocusWindow(), but it could be done more neatly.
See amended "nav_flattened" test.

docs/CHANGELOG.txt

@@ -134,6 +134,8 @@ Other changes:
     - Multi-Select (checkboxes)
     - Multi-Select (multiple scopes)
     - Multi-Select (advanced)
+- Nav: fixed clicking window decorations (e.g. resize borders) from losing focused item when
+  within a child window using ImGuiChildFlags_NavFlattened.
 - Clipper: added SeekCursorForItem() function. When using ImGuiListClipper::Begin(INT_MAX) you can
   can use the clipper without knowing the amount of items beforehand. (#1311)
   In this situation, call ImGuiListClipper::SeekCursorForItem(items_count) as the end of your iteration

imgui.h

@@ -28,7 +28,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM >= 12345')
 #define IMGUI_VERSION       "1.91.0 WIP"
-#define IMGUI_VERSION_NUM   19097
+#define IMGUI_VERSION_NUM   19098
 #define IMGUI_HAS_TABLE
 
 /*

imgui_widgets.cpp

@@ -567,9 +567,15 @@ bool ImGui::ButtonBehavior(const ImRect& bb, ImGuiID id, bool* out_hovered, bool
                     SetActiveID(id, window);
                     g.ActiveIdMouseButton = mouse_button_clicked;
                     if (!(flags & ImGuiButtonFlags_NoNavFocus))
+                    {
                         SetFocusID(id, window);
                         FocusWindow(window);
                     }
+                    else
+                    {
+                        FocusWindow(window, ImGuiFocusRequestFlags_RestoreFocusedChild); // Still need to focus and bring to front, but try to avoid losing NavId when navigating a child
+                    }
+                }
                 if ((flags & ImGuiButtonFlags_PressedOnClick) || ((flags & ImGuiButtonFlags_PressedOnDoubleClick) && g.IO.MouseClickedCount[mouse_button_clicked] == 2))
                 {
                     pressed = true;
@@ -577,11 +583,17 @@ bool ImGui::ButtonBehavior(const ImRect& bb, ImGuiID id, bool* out_hovered, bool
                         ClearActiveID();
                     else
                         SetActiveID(id, window); // Hold on ID
+                    g.ActiveIdMouseButton = mouse_button_clicked;
                     if (!(flags & ImGuiButtonFlags_NoNavFocus))
+                    {
                         SetFocusID(id, window);
-                    g.ActiveIdMouseButton = mouse_button_clicked;
                         FocusWindow(window);
                     }
+                    else
+                    {
+                        FocusWindow(window, ImGuiFocusRequestFlags_RestoreFocusedChild); // Still need to focus and bring to front, but try to avoid losing NavId when navigating a child
+                    }
+                }
             }
             if (flags & ImGuiButtonFlags_PressedOnRelease)
             {