Feature/310 scrollspy playwright

[sarah-storm]

Closes #310

Adds playwright to scroll spy component. Also addresses issues discovered during playwright testing around the activation of elements when multiple spies are in the viewport at one time. Changes to logic are as follows:

• Top of viewport is reference for 'activation'. When an element touches or crosses the viewport it becomes active
• Clicking any spy links should activate them
• If you've reached the bottom of the page without naturally activating the last spy, it will be activated

[mjbp]

Looks good to me.

Ran it in a current client project with a scroll margin with a rootMargin set and worked fine too.