Intl.RelativeTimeFormat: Add some tests for format, formatToParts, and resolvedOptions.

...ntl402/RelativeTimeFormat/prototype/format/unit-plural.js

...2/RelativeTimeFormat/prototype/format/value-non-finite.js

...tl402/RelativeTimeFormat/prototype/format/value-symbol.js

...RelativeTimeFormat/prototype/formatToParts/unit-plural.js

...iveTimeFormat/prototype/formatToParts/value-non-finite.js

...elativeTimeFormat/prototype/formatToParts/value-symbol.js

...2/RelativeTimeFormat/prototype/resolvedOptions/caching.js

...l402/RelativeTimeFormat/prototype/resolvedOptions/type.js