`nav` element test

Pass Criteria

#1: Element is supported
#2: Correct HTML and Core Accessibility API mappings
#3: Correct Accessible Name & Description Calculation

Reference

Test nv-001: `nav` element

Test nv-002: `nav` with `aria-label`

Test nv-003: `nav` with `aria-labelledby`

Test nv-004: `nav` element with `title` attribute

Test nv-005: `nav` with `aria-describedby`

Test nv-006: `nav` with `aria-label` & `title` attributes