Partially revert https://commits.webkit.org/258215@main. It turns out that WebKit whitespace handling for custom properties (where whitespace is always trimmed) is correct per https://drafts.csswg.org/css-syntax-3/#consume-declaration and this applies to initial-value too. This is test by imported/w3c/web-platform-tests/css/css-syntax/declarations-trim-whitespace.html which we pass and other engines fail. Update the @property tests to the spec.
<rdar://problem/103636334>
Pull request: https://github.com/WebKit/WebKit/pull/8003
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/37647
Committed 258245@main (4f0ccda88791): <https://commits.webkit.org/258245@main> Reviewed commits have been landed. Closing PR #8003 and removing active labels.