Add tests for well-known Symbol: @@toStringTag

test/built-ins/ArrayBuffer/prototype/Symbol.toStringTag.js

...eratorPrototype/Symbol.toStringTag/property-descriptor.js

test/built-ins/DataView/prototype/Symbol.toStringTag.js

...ilt-ins/GeneratorFunction/prototype/Symbol.toStringTag.js

test/built-ins/GeneratorPrototype/Symbol.toStringTag.js

test/built-ins/JSON/Symbol.toStringTag.js

test/built-ins/Map/prototype/Symbol.toStringTag.js

test/built-ins/MapIteratorPrototype/Symbol.toStringTag.js

test/built-ins/Math/Symbol.toStringTag.js

...built-ins/Object/prototype/toString/get-symbol-tag-err.js

...built-ins/Object/prototype/toString/symbol-tag-non-str.js

...uilt-ins/Object/prototype/toString/symbol-tag-override.js

test/built-ins/Object/prototype/toString/symbol-tag-str.js

test/built-ins/Promise/prototype/Symbol.toStringTag.js

test/built-ins/Set/prototype/Symbol.toStringTag.js

test/built-ins/SetIteratorPrototype/Symbol.toStringTag.js

test/built-ins/StringIteratorPrototype/Symbol.toStringTag.js

...built-ins/Symbol/prototype/@@toStringTag/@@toStringTag.js

test/built-ins/Symbol/prototype/Symbol.toStringTag.js

test/built-ins/Symbol/toStringTag/prop-desc.js