Bug 1564659 [wpt PR 17441] - [css-lists] list-style-image computed value, a=testonly

Automatic update from web-platform-tests
[css-lists] list-style-image computed value (#17441)

list-style-image supports image, including gradients
https://drafts.csswg.org/css-lists-3/#propdef-list-style-image

Colors and lengths in gradients are computed in computed style
results.
w3c/csswg-drafts#4042

calcs giving negative radii are clamped to 0.
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wpt-commits: 11984f1d160b7454b2d8d1e177d1e48b9db750e1
wpt-pr: 17441

UltraBlame original commit: 151290fe24f003be50293ac1cc4a21e4911fe6e8

Author: marco-c