Consider adding "microsecond" and "nanosecond" to the set of sanctioned unit identifiers

[anba]

For Intl.DurationFormat we need to include the CLDR data for "microsecond" and "nanosecond" anyway, so we should consider adding both units to the set of sanctioned unit identifiers.

[ray007]

If SI unit prefixes were not part of the units, we'd not have this problem.

[FrankYFTang]

This issue is fixed by #708 that merged in last Nov already.