Library: Port 'Spinner' demo to Python (#712)

Author: UrtsiSantsi

src/Library/demos/Spinner/main.py

@@ -0,0 +1,20 @@
+import gi
+
+gi.require_version("Gtk", "4.0")
+from gi.repository import Gtk
+import workbench
+
+button: Gtk.Button = workbench.builder.get_object("button")
+spinner: Gtk.Spinner = workbench.builder.get_object("spinner")
+
+
+def button_clicked(_widget):
+    if spinner.get_spinning():
+        button.set_icon_name("media-playback-start")
+        spinner.set_spinning(False)
+    else:
+        button.set_icon_name("media-playback-pause")
+        spinner.set_spinning(True)
+
+
+button.connect("clicked", button_clicked)