GTK: Delay IME context focus to fix IME input bugs when there're embedded CEF window.

We need to delay IME context focus in, to avoid confusing the IME framework(be it ibus or fcitx) where the
IME focus really is when there're embedded CEF windows.

Author: 徐扬斌

src/gtk/window.cpp

@@ -4722,9 +4722,6 @@ bool wxWindowGTK::GTKHandleFocusIn()
                "handling focus_in event for %s",
                wxDumpWindow(this));
 
-    if (m_imContext)
-        gtk_im_context_focus_in(m_imContext);
-
     gs_currentFocus = this;
 
     if ( gs_pendingFocus )
@@ -4755,6 +4752,18 @@ bool wxWindowGTK::GTKHandleFocusIn()
 
     GTKProcessEvent(eventFocus);
 
+    if (m_imContext)
+    {
+        // delay gtk_im_context_focus_in to avoid timing conflict with IME framework(fcitx)
+        g_idle_add([](gpointer data) -> gboolean {
+            GtkIMContext* context = static_cast<GtkIMContext*>(data);
+            if (context) {
+                gtk_im_context_focus_in(context);
+            }
+            return G_SOURCE_REMOVE; // only run once
+        }, m_imContext);
+    }
+
     return retval;
 }