Update the screen readers about change in result count.

Problem/Motivation

As discussed in the Accessibility meeting
Currently, the result count + additional info are in an <output> element. This is an active element that conveys info to screen readers. However, it will only convey that information when the content of the element changes. This results in a problem - if a filter/search change has the same number of results, the <output> contents do not change, and thus nothing is conveyed to the screen reader.

For example Choose "accessibility" category , amd set the filters to "covered by a security policy" and "maintained". Toggle the "development status" and the result count will be the same. Currently that means the screenreader says nothing, but a screenreader user needs to know the number of results after they choose a new filter, even if the result count is the same. It's relevant information and it's absence could lead to the impression that the operation did not complete.

Steps to reproduce

Proposed resolution

Instead of relying on <output>, use Drupal.announce() for greater control over the information conveyed.

Remaining tasks

• ✅ File an issue about this project
• ☐ Manual Testing
• ☐ Code Review
• ☐ Accessibility Review
• ☐ Automated tests needed/written?