[amp-story] AmpStory runtime replacing vh/vw in css classnames

## What's the issue?
Looks like the amp runtime is being a little over aggressive in it's vh/vw replacements as it's replacing the pattern `/\d+v[hw]/i` in class names effectively breaking the selectors and css

i.e. `.cardText__1VW` gets turned into `.cardText__calc(1 * var(--story-page-vw))`

## How do we reproduce the issue?
Add a class to an element with the pattern above and render the html in amp

## What browsers are affected?
All

## Which AMP version is affected?
Seemingly just amp stories, but no clue where else this could be affecting