offsetPercentage property
The offsets as a percentage of the parent FResizable's size.
For example, if the offsets are (200, 400), and the FResizable's size is 500, offsetPercentage will be
(0.4, 0.8).
Implementation
({double min, double max}) get offsetPercentage => (min: offset.min / extent.total, max: offset.max / extent.total);