[gtkmm] Gtk::Widget: Update the class documentation

[Kjell Ahlstedt <kjellahl src gnome org>]

commit e5118082d5a452adc0e1dfa2312920d6f9b7476d
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Wed Jun 29 11:57:54 2022 +0200

    Gtk::Widget: Update the class documentation
    
    Mention event controllers instead of the event signals
    that don't exist in gtkmm4.

 gtk/src/widget.hg | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)
---
diff --git a/gtk/src/widget.hg b/gtk/src/widget.hg
index 2187daa8..0b6974cc 100644
--- a/gtk/src/widget.hg
+++ b/gtk/src/widget.hg
@@ -77,21 +77,16 @@ typedef Gdk::Rectangle Allocation;
  */
 
 //TODO: Deal with the GtkObject->GObject change:
-/** Abstract Widget (Base class for all widgets)
+/** Abstract %Widget (Base class for all widgets)
  *
  * As the base class of all widgets this contains all of the properties
- * and methods common to all widgets.  It is an abstract class that
- * can not be instantiated.
+ * and methods common to all widgets. It manages the widget lifecycle, layout,
+ * states and style. It is an abstract class that cannot be instantiated.
  *
- * Important part of widgets are the *_event signals and virtual methods
- * that every widget have. Those are events coming directly from gdk and
- * thus also from XLib. By overriding those virtual methods you can
- * trap everything a widget can ever do.
- * In order to capture events from a widget, the event mask must
- * first be set with ().
- *
- * Only widgets with a Gdk::Surface on the server side are allowed to
- * capture events.
+ * An important part of widgets are events that can be trapped by adding
+ * event controllers with add_controller(). Those are events coming directly
+ * from gdk. By using event controllers you can trap everything a widget
+ * can ever do.
  */
 class GTKMM_API Widget
 : public Object,