video + track element test

Pass Criteria

• #1: Elements are supported
• #2: Elements have correct HTML and Core Accessibility API mappings
• #3: At least one subtitle format is supported (WebVTT or TTML)
• #4: Controls are keyboard accessible:
  • #4.1: Controls MUST be focusable
  • #4.2: MUST be able to activate controls, including any child menu/controls