`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