[bug] `va-accordion` expand/collapse all button visibility

[Mottie]

Bug Report

• [x] I’ve searched for any related issues and avoided creating a duplicate issue.

What happened

I found 2 minor issues with the va-accordion web component.

• If there is only one va-accordion-item within this wrapper, the "Expand all"/"Collapse all" button should be hidden, or update the documentation to describe the usage for only one va-accordion-item
• If all of the va-accordion-item elements inside the va-accordion are not rendered (or hidden), the "Expand all"/"Collapse all" button should also be hidden.

Codesandbox demo showing the issues described above

What I expected to happen

Hide the "Expand all"/"Collapse all" button when one, or less, va-accordion-item are visible within the wrapper

Reproducing

• Formation version: Latest
• Device: (e.g. iPhone 8, Macbook): All
• Browser: (e.g. Firefox, IE 11): All

Steps to reproduce:

1. In the codesandbox demo, toggle the checkbox that shows and hides the va-accordion-item
2. Note that the "Expand all"/"Collapse all" button is always visible

[k80bowman]

In the Slack thread on this support issue, @bkjohnson noted that he thought we had some guidance saying that an accordion should have two or more items, but it doesn't seem to be currently in our guidance.

@GnatalieH or @humancompanion-usds, do you have any thoughts on this?

[GnatalieH]

@k80bowman I also believe we should update our guidance to say that accordions should always have two or more items. If someone needs a single expandable content element, they can use Additional info. CC @humancompanion-usds

[humancompanion-usds]

@Mottie - Can you point us to the instance of a single accordion so I can have a look? Thanks.

Neither we nor USWDS have guidance around a minimum number of Accordions one has to have. I've used single accordions in the past (though I did not have an Additional Info component). I can imagine a use case for a single accordion given that it has much more visual presence than Additional info. Regardless, the 2nd issue mentioned still sounds like a bug either way.

[Mottie]

https://staging.va.gov/decision-reviews/higher-level-review/#find-addresses-for-other-benef-8622

[bkjohnson]

Since that template is setting data-multiselectable based on a CMS value, a quick fix could be to add the open-single prop to the accordion if entity.fieldCollapsiblePanelMulti is false.

The "Expand all" button isn't added if openSingle is truthy.