DS-2410: Add VRT and E2E test for ontario-accordion

[MeaghanCarrieres]

Adds Visual Regression Testing (VRT) and End-to-End (E2E) test coverage for the ontario-accordion component in the NextJS app.

What was added

• Updated the ontario-accordion test page to:
  • Include stable id attributes for reliable test targeting
  • Cover edge and negative cases (e.g. invalid accordion-data prop, missing expand-collapse-button prop)
• Added VRT tests to validate:
  • Default rendering variants
  • Expanded/collapsed states
  • Custom expand/collapse labels
  • Focus states
• Added E2E tests to validate:
  • Accordion open/close behaviour
  • Expand all / collapse all logic
  • Accessibility state updates and labels
  • Handling of invalid input
• Introduced small accordion event utilities to:
  • Capture and assert accordionChange events in a framework-agnostic way
  • Keep tests readable and consistent with existing Playwright patterns