[To Do] Add visual regression (Backstop) tests to Less

[matthew-dean]

This came up for fixes to svg-gradient() (#3261). There are no automated visual regression tests, so it might be good to do so for functions that create visual assets. See: https://github.com/garris/BackstopJS

[Bruce-Hopkins]

Is this still relevent? Can I pick this up?

[khareyash05]

Is this open to work @matthew-dean ?

[matthew-dean]

Yep! I'm not sure if BackstopJS is still the best current solution, but yes I think it's still needed.