`fieldset` element with `legend` element

Pass Criteria

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

Reference

Test flgnd-001: `fieldset` element with `legend` element

Test flgnd-002: `fieldset` element with `legend` element containing a `h2` element

Test flgnd-003: `fieldset` element with `aria-labelledby`, with `legend` element

Test flgnd-004: `fieldset` element, `legend` element with `aria-label`