Determines when the leaflet will fold.
If set to adw.types.FoldThresholdPolicy.Minimum, it will only fold when the children cannot fit anymore. With adw.types.FoldThresholdPolicy.Natural, it will fold as soon as children don't get their natural size.
This can be useful if you have a long ellipsizing label and want to let it ellipsize instead of immediately folding.
Deprecated: See the migration guide
Set foldThresholdPolicy property.