Wait for class testing utilities

[MrTeale]

As more and more CSS libraries and frameworks are using utility classes, there is a growing need for people to check an elements class attribute contains or equals a value. I am currently in this circumstance building a set of custom AIO components utilising TailwindCSS and FontAwesome icons.

My reasoning for making this addition was to check a callback had successfully changed the icon within a div. FontAwesome uses the ::before pseudo-element with a content css property to contain the unicode character of the icon. The process to access psuedo-elements within Selenium is not the most developer friendly method (example here) but if they're being created by classes, why not just check and wait for those?

The testing documentation (located here) would need to be updated to include these new options under Browser APIs.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • Add wait_for_class_to_equal
  • Add wait_for_contains_class
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added entry in the CHANGELOG.md

[alexcjohnson]

Very nice addition @MrTeale! 💃 after my two minor comments are addressed.

[MrTeale]

Thanks @alexcjohnson! I've made those changes and should be 💃 now