Fix various bogus WPTs that test wrong calc serialization.
https://drafts.csswg.org/css-values-4/#calc-serialize:
> Sort the terms in the following order:
> The number, if present
> The percentage, if present
> The dimensions, ordered by their units ASCII case-insensitive alphabetically
> Comparison, trigonometric and exponential functions, in the order they appeared in the original expression.
So em goes before px. I filed https://github.com/w3c/csswg-drafts/issues/4129 on
the second part of that algorithm not matching any browser.
These are tests that are marked as only failing in Firefox because we're the
only following the spec. #funtimes
Differential Revision: https://phabricator.services.mozilla.com/D38593
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1567349
gecko-commit: 0bbd8e64cb9cbef70d12bcf502a8948882b63fe9
gecko-integration-branch: central
gecko-reviewers: heycam