[SelectPanel] Fix result count in screen reader announcements

[camertron]

What are you trying to accomplish?

This PR fixes an issue causing SelectPanels to announce an incorrect number of items after filtering. It also switches to using the awesome <live-region> element.

Integration

No changes necessary in production.

List the issues that this change affects.

Fixes https://github.com/github/primer/issues/4369

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

What approach did you choose and why?

I changed the code to only consider visible items, and switched to the <live-region> element: https://github.com/primer/live-region-element.

Accessibility

• No new axe scan violation - This change does not introduce any new axe scan violations.

Merge checklist

• Added/updated tests
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[changeset-bot]

🦋 Changeset detected

Latest commit: 03f4e83

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/view-components	Patch

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[jonrohan]

👍🏻