Define DefaultLocale and DefaultTimeZone

[annevk]

It seems that https://tc39.es/ecma402/ expects host environments to return something for these.

Probably need to abstract navigator.language for the former, not sure about the latter.

(For the latter, #3047 is relevant as well.)

cc @littledan @nicolo-ribaudo

[ryzokuken]

DefaultTimeZone might get moved around when we merge Temporal, but needs to be defined nonetheless.

[TRCREO]

OK . Thanks . Whats Temporal ?