Fix Duration precision bug in polyfill, Duration+Instant precision bug in spec. (#1405)
Fix Duration precision bug in polyfill, Duration+Instant precision bug in spec. (#1405)

Same bug as #1351 in another place, with corresponding spec fixes for both #1351 and #1404.

Fixes #1404.
js-temporal/temporal-polyfill,js-temporal/temporal-polyfill,js-temporal/temporal-polyfill