It is possible for a custom property to animate between two lists of mismatching types, for instance if it's defined as `<number>+ | <transform-list>`. In that case, we must use discrete blending.
rdar://104814851
Pull request: https://github.com/WebKit/WebKit/pull/9307
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/38252
Committed 259557@main (30df2fedb438): <https://commits.webkit.org/259557@main> Reviewed commits have been landed. Closing PR #9307 and removing active labels.
Committed 259548.71@safari-7615-branch (d0ad85a37b8d): <https://commits.webkit.org/259548.71@safari-7615-branch> Reviewed commits have been landed. Closing PR #371 and removing active labels.