Bug 1834164 - Serialize NaN and infinity numbers r=emilio

Added NaN/inf serialization of <number> and changed calc() code to not
remove NaN/infinity in code using it.

This change is unfortunately imperfect as some things using <number>
still refuse to serialize NaN/infinity for some reason (scale()?), but
this bug/patch is just for <number> so leaving that out of scope for this.

Also added new WPT test file for number NaN/inf serialization based
on existing serialization tests (all pass already!).

5 other WPT subtests now newly pass.

Differential Revision: https://phabricator.services.mozilla.com/D178587