Add the Intl DateTimeFormat polyfill for space scripts without overwriting other Intl classes

[daniel-michel]

The Intl polyfill provided by js-temporal only includes the DateTimeFormat class. Because the global Intl is replaced with it, the other classes provided by Intl are not accessible.

I changed it, so the Intl polyfill gets applied to the global Intl, therefore only replacing the DateTimeFormat.

[zefhemel]

Nice!