In the very common case that no special constructor options are provided
for the Intl.Collator when calling localeCompare() on a string, we can
cache and reuse a default-constructed Intl.Collator, saving lots of time
and space.
This shaves a fair bit of load time off of https://wpt.fyi/ where they
use Array.prototype.sort() and localeCompare() to sort a big JSON thing.
Time spent in sort():
- Before: 1656 ms
- After: 135 ms
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