Revert "plugin-manager: Drop MetaPluginClass.xevent_filter"

This reverts commit 917526ee9d.

As it is currently used by GNOME Kiosk, until upstream figures out
how to replace that code path, let us revert the commit

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3652>

src/backends/x11/meta-backend-x11.c

@@ -348,7 +348,9 @@ handle_host_xevent (MetaBackend *backend,
   MetaBackendX11Private *priv = meta_backend_x11_get_instance_private (x11);
   ClutterBackend *clutter_backend = meta_backend_get_clutter_backend (backend);
   ClutterSeat *seat = clutter_backend_get_default_seat (clutter_backend);
+  MetaContext *context = meta_backend_get_context (backend);
   gboolean bypass_clutter = FALSE;
+  MetaDisplay *display;
 
   switch (event->type)
     {
@@ -363,7 +365,19 @@ handle_host_xevent (MetaBackend *backend,
 
   XGetEventData (priv->xdisplay, &event->xcookie);
 
-  bypass_clutter = meta_backend_x11_handle_host_xevent (x11, event);
+  display = meta_context_get_display (context);
+  if (display)
+    {
+      MetaCompositor *compositor = display->compositor;
+      MetaPluginManager *plugin_mgr =
+        meta_compositor_get_plugin_manager (compositor);
+
+      if (meta_plugin_manager_xevent_filter (plugin_mgr, event))
+        bypass_clutter = TRUE;
+    }
+
+  bypass_clutter = (meta_backend_x11_handle_host_xevent (x11, event) ||
+                    bypass_clutter);
 
   if (event->type == (priv->xsync_event_base + XSyncAlarmNotify))
     handle_alarm_notify (backend, (XSyncAlarmNotifyEvent *) event);

src/compositor/meta-plugin-manager.c

@@ -26,6 +26,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "backends/x11/meta-clutter-backend-x11.h"
 #include "compositor/compositor-private.h"
 #include "compositor/meta-module.h"
 #include "core/meta-inhibit-shortcuts-dialog-default-private.h"
@@ -331,6 +332,15 @@ meta_plugin_manager_filter_keybinding (MetaPluginManager *plugin_mgr,
   return FALSE;
 }
 
+gboolean
+meta_plugin_manager_xevent_filter (MetaPluginManager *plugin_mgr,
+                                   XEvent            *xev)
+{
+  MetaPlugin *plugin = plugin_mgr->plugin;
+
+  return _meta_plugin_xevent_filter (plugin, xev);
+}
+
 void
 meta_plugin_manager_confirm_display_change (MetaPluginManager *plugin_mgr)
 {

src/compositor/meta-plugin-manager.h

@@ -70,6 +70,11 @@ gboolean meta_plugin_manager_switch_workspace (MetaPluginManager   *mgr,
 gboolean meta_plugin_manager_filter_keybinding (MetaPluginManager  *mgr,
                                                 MetaKeyBinding     *binding);
 
+gboolean meta_plugin_manager_xevent_filter (MetaPluginManager *mgr,
+                                            XEvent            *xev);
+gboolean _meta_plugin_xevent_filter (MetaPlugin *plugin,
+                                     XEvent     *xev);
+
 void     meta_plugin_manager_confirm_display_change (MetaPluginManager *mgr);
 
 gboolean meta_plugin_manager_show_tile_preview (MetaPluginManager *mgr,

src/compositor/meta-plugin.c

@@ -30,8 +30,12 @@
 #include "meta/meta-plugin.h"
 
 #include <string.h>
+#include <X11/Xlib.h>
+#include <X11/extensions/Xfixes.h>
+#include <X11/extensions/shape.h>
 
 #include "backends/meta-monitor-manager-private.h"
+#include "backends/x11/meta-clutter-backend-x11.h"
 #include "compositor/compositor-private.h"
 #include "compositor/meta-window-actor-private.h"
 #include "compositor/meta-plugin-manager.h"
@@ -67,6 +71,18 @@ meta_plugin_get_info (MetaPlugin *plugin)
   return NULL;
 }
 
+gboolean
+_meta_plugin_xevent_filter (MetaPlugin *plugin,
+                            XEvent     *xev)
+{
+  MetaPluginClass *klass = META_PLUGIN_GET_CLASS (plugin);
+
+  if (klass->xevent_filter)
+    return klass->xevent_filter (plugin, xev);
+  else
+    return FALSE;
+}
+
 void
 meta_plugin_switch_workspace_completed (MetaPlugin *plugin)
 {

src/meta/meta-plugin.h

@@ -21,6 +21,7 @@
 
 #pragma once
 
+#include <X11/extensions/Xfixes.h>
 #include <gmodule.h>
 
 #include "clutter/clutter.h"
@@ -51,6 +52,7 @@ typedef struct _MetaPluginInfo    MetaPluginInfo;
  * as if the effect terminated naturally
  * @kill_switch_workspace: virtual function called when the workspace-switching
  * effect needs to be killed prematurely
+ * @xevent_filter: virtual function called when handling each event
  * @keybinding_filter: virtual function called when handling each keybinding
  * @plugin_info: virtual function that returns information about the
  * #MetaPlugin
@@ -163,6 +165,20 @@ struct _MetaPluginClass
    */
   void (*kill_switch_workspace)    (MetaPlugin     *plugin);
 
+  /**
+   * MetaPluginClass::xevent_filter:
+   * @event: (type xlib.XEvent):
+   *
+   * Virtual function called when handling each event.
+   *
+   * Returns: %TRUE if the plugin handled the event type (i.e., if the return
+   * value is %FALSE, there will be no subsequent call to the manager
+   * completed() callback, and the compositor must ensure that any appropriate
+   * post-effect cleanup is carried out.
+   */
+  gboolean (*xevent_filter) (MetaPlugin       *plugin,
+                             XEvent           *event);
+
   /**
    * MetaPluginClass::keybinding_filter:
    * @binding: a #MetaKeyBinding