[css-box-4] Does margin-trim affect the computed values of margins?

[bfgeek]

While discussing #11325 (comment) is was mentioned that margin-trim shouldn't affect the getComputedStyle of margins.

However in WPT there are a bunch of tests asserting this behaviour.
https://wpt.fyi/results/css/css-box/margin-trim/computed-margin-values?label=master&label=experimental&aligned

For most layout modes this is ~fine, however for block layout this means that theoretically the getComputedStyle of margins wouldn't round trip I think?

cc/ @fantasai