On decorator (#2453)

* Add on decorator

* decorator code

* docs for on decorator

* Examples

* test errors

* simplify listing

* words

* changelog

* Update docs/guide/events.md

Co-authored-by: Dave Pearson <davep@davep.org>

* Update docs/guide/events.md

Co-authored-by: Dave Pearson <davep@davep.org>

* Update docs/examples/events/on_decorator.css

Co-authored-by: Rodrigo Girão Serrão <5621605+rodrigogiraoserrao@users.noreply.github.com>

* Update docs/guide/events.md

Co-authored-by: Rodrigo Girão Serrão <5621605+rodrigogiraoserrao@users.noreply.github.com>

* rewording

* comment

* clarification

* Added note

---------

Co-authored-by: Dave Pearson <davep@davep.org>
Co-authored-by: Rodrigo Girão Serrão <5621605+rodrigogiraoserrao@users.noreply.github.com>

docs/examples/events/on_decorator01.py

@@ -0,0 +1,27 @@
+from textual import on
+from textual.app import App, ComposeResult
+from textual.widgets import Button
+
+
+class OnDecoratorApp(App):
+    CSS_PATH = "on_decorator.css"
+
+    def compose(self) -> ComposeResult:
+        """Three buttons."""
+        yield Button("Bell", id="bell")
+        yield Button("Toggle dark", classes="toggle dark")
+        yield Button("Quit", id="quit")
+
+    def on_button_pressed(self, event: Button.Pressed) -> None:
+        """Handle all button pressed events."""
+        if event.button.id == "bell":
+            self.bell()
+        elif event.button.has_class("toggle", "dark"):
+            self.dark = not self.dark
+        elif event.button.id == "quit":
+            self.exit()
+
+
+if __name__ == "__main__":
+    app = OnDecoratorApp()
+    app.run()