This exposes an existing issue with interpolation where it is not clear
in what situations zero-valued dimensions should be excluded from the
interpolated value of a dimension-percentage mix (e.g. `calc(50% + 0px)`
vs `50%`) - but this is just a serialization issue as both
representations are resolved to the same used value
Some subtests changed in response to this CSSWG resolution:
https://github.com/w3c/csswg-drafts/issues/11494#issuecomment-2675800489
Basically, `border-style: none` now affects the used value of
`border-width`, not the computed value. (And the same for `outline`
properties.)
This affects way more tests than I expected because
interpolation-testcommon.js now adds tests for composition.
