Emitted when one or more D-Bus properties on proxy changes.
The local cache has already been updated when this signal fires. Note that both changed_properties and
invalidated_properties are guaranteed to never be null (either may be empty though).
If the proxy has the flag g_dbus_proxy_flags_get_invalidated_properties set, then
invalidated_properties will always be empty.
This signal corresponds to the `PropertiesChanged` D-Bus signal on the `org.freedesktop.DBus.Properties` interface.
| changed_properties |
A Variant containing the properties that changed (type: `a{sv}`) |
| invalidated_properties |
A null terminated array of properties that was invalidated |