Add tests for additional uses of @@toPrimitive (#666)

test/built-ins/Date/value-get-symbol-to-prim-err.js

test/built-ins/Date/value-symbol-to-prim-err.js

test/built-ins/Date/value-symbol-to-prim-invocation.js

test/built-ins/Date/value-symbol-to-prim-return-obj.js

test/built-ins/Date/value-symbol-to-prim-return-prim.js

...anguage/expressions/addition/coerce-symbol-to-prim-err.js

.../expressions/addition/coerce-symbol-to-prim-invocation.js

.../expressions/addition/coerce-symbol-to-prim-return-obj.js

...expressions/addition/coerce-symbol-to-prim-return-prim.js

test/language/expressions/addition/get-symbol-to-prim-err.js