QSortFilterProxyModel did not emit dataChanged when calling
setSourceModel() after modifying the source model.
QSortFilterProxyModel::setSourceModel and
QSortFilterProxyModelPrivate::_q_sourceReset(), _q_clearMapping
is called to delete the source_index_mapping. They also need to
call create_mapping function to re-create it.
Fixes: QTBUG-87781
Pick-to: 5.15
Change-Id: Idbe34696c9d3a2fbf354b653c870bac61378811d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
8455bfee76