Determines when the squeezer will switch children.
If set to `ADW_FOLD_THRESHOLD_POLICY_MINIMUM`, it will only switch when the visible child cannot fit anymore. With `ADW_FOLD_THRESHOLD_POLICY_NATURAL`, it will switch as soon as the visible child doesn'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 switching.