Import css/css-text-decor/text-shadow folder from WPT
Pull request: https://github.com/WebKit/WebKit/pull/6702
Committed 256926@main (e8878aaeea63): <https://commits.webkit.org/256926@main> Reviewed commits have been landed. Closing PR #6702 and removing active labels.
<rdar://problem/102598776>