Return QMetaObject.Connection from SignalInstance.connect()

I would like it if `my_qobject.a_signal.connect()` returned something that could be passed to `my_qobject.a_signal.disconnect()`.  Presently a `bool` is returned.  `QObject::connect()` returns a `QMetaObject.Connection`.  

https://doc.qt.io/qt-5/qobject.html#connect

https://doc.qt.io/qt-5/qmetaobject-connection.html

At the link there are a few comments about this for PyQt5 which did eventually add this.

https://riverbankcomputing.com/pipermail/pyqt/2017-December/039853.html

Perhaps this should be a suggestion but I feel it is reasonable to at least initially submit as a bug since this seems to not match the regular C++ connection methods.  I presume this is applicable to 'all' versions and platforms but reported the ones I am presently running and have observed it on.