Add tests for well-known Symbol: @@toPrimitive

...rototype/Symbol.toPrimitive/hint-default-first-invalid.js

...ype/Symbol.toPrimitive/hint-default-first-non-callable.js

.../prototype/Symbol.toPrimitive/hint-default-first-valid.js

...prototype/Symbol.toPrimitive/hint-default-no-callables.js

...prototype/Symbol.toPrimitive/hint-number-first-invalid.js

...type/Symbol.toPrimitive/hint-number-first-non-callable.js

...e/prototype/Symbol.toPrimitive/hint-number-first-valid.js

.../prototype/Symbol.toPrimitive/hint-number-no-callables.js

...prototype/Symbol.toPrimitive/hint-string-first-invalid.js

...type/Symbol.toPrimitive/hint-string-first-non-callable.js

...e/prototype/Symbol.toPrimitive/hint-string-first-valid.js

.../prototype/Symbol.toPrimitive/hint-string-no-callables.js