Pivot facet field list aria roles are incorrect

[seanaery]

This accessibility issue is flagged by Axe DevTools when a Pivot Field is expanded.

<li> elements must be contained in a <ul> or <ol>

https://dequeuniversity.com/rules/axe/4.10/listitem?application=AxeChrome

To solve this problem, you need to fix the following: List item parent element has a role that is not role="list"

It appears the pivot-facet uls currently have role="group" which makes them not semantically treated as lists; and because the lis do not currently have a role, they expect to be members of a list.

If Blacklight core were to follow the same practice as blacklight-hierarchy (which does not have this issue), we'd use role="group" or role="tree" on the uls, and role="treeitem" on the lis for nested facets. See examples.