Bug 1775116 - Use last mouse press event to trigger native menus. r=stransky

Otherwise (sometimes?) Mutter sends us an "Esc" key event on button
release (why tho?) which causes Gtk to hide the widget.

This is ironically trivial to fix after the drag service fix.

Differential Revision: https://phabricator.services.mozilla.com/D149871

widget/gtk/NativeMenuGtk.cpp

@@ -7,6 +7,7 @@
 #include "mozilla/dom/Document.h"
 #include "mozilla/dom/DocumentInlines.h"
 #include "mozilla/dom/XULCommandEvent.h"
+#include "mozilla/WidgetUtilsGtk.h"
 #include "mozilla/EventDispatcher.h"
 #include "nsPresContext.h"
 #include "nsIWidget.h"
@@ -380,7 +381,7 @@ void NativeMenuGtk::ShowAsContextMenu(nsPresContext* aPc,
   const GdkRectangle rect = {gdkPos.x, gdkPos.y, 1, 1};
   auto openFn = GetPopupAtRectFn();
   openFn(GTK_MENU(mNativeMenu.get()), win, &rect, GDK_GRAVITY_NORTH_WEST,
-         GDK_GRAVITY_NORTH_WEST, nullptr);
+         GDK_GRAVITY_NORTH_WEST, GetLastMousePressEvent());
 
   RefPtr pin{this};
   FireEvent(eXULPopupShown);