[FEATURE] Display Squares as an option in SLDS2 - all Icons are rounded.

[JodieM]

Is your feature request related to a problem? Please describe.
This is just an annoyance with SLDS2 and whilst we are looking at #188 if we can look at this too, that would be great.

Describe the solution you'd like
The current display options on the LWC are Base and Circle. In SLDS 2, there is no difference between the two - see SLDS2 Variants

Describe alternatives you've considered
Due to the fact that our Icons are based off the Avatar Component SLDS2 doesn't allow for squares, but the Icons page on SLDS2 says "SLDS 2 updates the background shape of standard icons to a circle."

So I don't have an alternative other than bypass SLDS2 if we can, to put back square icons. Is it a big enough deal? I don't know.