st/button: Consider touch sequences for ::pressed state

We do notify on the ::pressed property after touch begin/end and
recording the event sequence, but we do not return the correct value
if the button was triggered via touch.

Consider the event sequence also in the ::pressed getter, so the
button is considered pressed.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1774>

src/st/st-button.c

@@ -432,7 +432,7 @@ st_button_get_property (GObject    *gobject,
       g_value_set_boolean (value, priv->is_checked);
       break;
     case PROP_PRESSED:
-      g_value_set_boolean (value, priv->pressed != 0);
+      g_value_set_boolean (value, priv->pressed != 0 || priv->press_sequence != NULL);
       break;