chore: refactor @shared/UsaIcon.jsx and test #4668

[sknep]

Changes proposed in this pull request:

• removed aria-hidden because node visibility ought to be determined by the role https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Attributes/aria-hidden
• Removed unnecessary aria-hidden and focusable props, using role to determine visibility and focusability
• focusable is now false by default, and only set to true for role="button" and role="link", per a11y guidelines
• replaced deprecated xlinkHref withhref USWDS-Site: Replaced deprecated xlink:href code with recommended use of href uswds/uswds-site#2926 and https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/xlink:href
• role must now be one of the following, suitable for icons: img, presentation, button, link, status, none https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles
• size must be one of the USWDS icon size options, 3-9 https://designsystem.digital.gov/components/icon/#component-variants-icon
• add tests per Add RTL tests to @shared/UsaIcon.jsx #4668

security considerations

• None, UI changes only

[cloud-gov-pages-operations]

🤖 This is an automated code coverage report

Total coverage (lines): 18.06%
Coverage diff: 0.12% 📈