Allow Max & Min Index of Polar Radius from a scanned feature

When finding a high point of a linear feature it's possible to use the Maxindex assignment relative to a specific axis. For example "maxindex(scan.x)". This will return the max value in X for that scan.

When scanning radial features and finding a max Polar Radius, one would expect to use "maxindex(scan.PR)" to return the max value for PR in that scan. Thus giving a high point of a radius for example.

This command doesn't work with polar radius.