fix(loaders): changed Dots and Spinner roles from progressbar to img

[jgorfine-zendesk]

Description

To make the Dots and Spinner components accessible to assistive tech users — and to make them conform to WCAG 2.1 Success Criterion 4.1.2 Name, Role, Value (level A) — this PR changes the SVG role from progressbar to img.

Detail

Spinner

Dots

Checklist

• 👌 design updates will be Garden Designer approved (add the designer as a reviewer)
• 🌐 demo is up-to-date (yarn start)
• ⬅️ renders as expected with reversed (RTL) direction
• 🤘 renders as expected with Bedrock CSS (?bedrock)
• 💂‍♂️ includes new unit tests. Maintain existing coverage (always >= 96%)
• ♿ tested for WCAG 2.1 AA accessibility compliance
• 📝 tested in Chrome, Firefox, Safari, and Edge