This allows us to give it a signal, which silences a qmllint warning.
While the engine does not actually need that currently, it is planned
that we want to slowly get away from supporting non-notifying bindable
properties.
This allows us to set max-warnigs to 0 for qmllint.
Pick-to: 6.10
Fixes: QTBUG-138176
Change-Id: I3221095f31639d90ebcc9d54fd4376cfb9140961
Reviewed-by: Olivier De Cannière <olivier.decanniere@qt.io>