Used to inform Agentry that a new height is desired for an autosizing field.
If the field is not autosizing, this request will be ignored. If it is autosizing and the extension can handle autosizing, Agentry will fire layout calculations and it might query the extension for the size again letting it know what its final width will be. See model:wantsViewHeightForWidth: (SMPOpenUIFieldAdapter-p) in the SMPOpenUIFieldAdapter protocol.