Create 'expand/collapse all' option for accordion

[bspeare]

Problem

Currently the accordion does not have an expand/collapse option for all accordion items: https://codepen.io/Sp00ky/pen/zBZZvq.

Proposed Solution

Add expand/collapse all option to accordions.

[bspeare]

@mjoneill Do you want to add anything to this issue?

[mjoneill]

@bspeare Just some prior art/examples. I think you can find explanations/opinions for why they are helpful/useful from a number of sources.

Here are some examples in the wild (not necessarily saying these are awesome accordions... just that they have the functionality we're discussing):

• https://www.adea.org/faq/
• https://www.fairchild.af.mil/FAQ/
• https://www.joinallofus.org/faq (<--- swaps expand/hide on activation)
• https://open.berkeley.edu/guides/site-builders-guide/faq-display
• https://www.womcom.org/content.aspx?page_id=274&club_id=903060 (<--- please don't emulate this implementation. it's probably a verified antipattern. ;P )