[web-animations-2] Should CSSNumericValue number values be allowed for setting start and current time?

[Calme1709]

Both Chrome and WebKit support setting the start/current time of a time-based animation to a CSSNumericValue number value (i.e. CSSNumericValue.parse("3000")) and this is explicitly tested in WPT for both current time and start time.

This is contrary to the spec which in the procedure to validate a CSSNumberish time only allows CSSNumericValues with duration units:

If all of the following conditions are true:
- The animation is not associated with a progress-based timeline, and
- time is a CSSNumericValue, and
- the units of time are not duration units:
throw a TypeError.
return false.