Margin visualizer incorrectly shows inwards

[jasmussen]

Extracting from #44484 (comment): there appears to be an issue with the margin visualization, where if you apply margin to, for example, a group block, the visualization resizes inwards as if to indicate padding, instead of outwards. GIF showing this:

In an older iteration, this worked as intended:

It isn't clear when this regression happened. I've seen it work prior to #44323, but it isn't clear that PR introduce the regression either, please see additional context here.

[talldan]

It is a bug in 6.1 so I've added it to the project board. It's most noticeable for me when adjusting the margin on the group within TT3's header.

[glendaviesnz]

This seems to be related to the clamp values that TT3 is using for spacing sizes, eg. clamp(7rem, 14vw, 11rem). If I replace these with simple rem values the margin visualiser works as expected. I will take a closer look and see if there is anyway of getting the clamp values into the format that the visualiser can cope with.