[SR-14384][SR-14974] Fix `Decimal.ulp`, `nextUp`, `nextDown`#3070

Merged

xwu merged 4 commits intoswiftlang:mainfrom

xwu:decimal-ulp-nextup-nextdown

Sep 8, 2021

Commits on Aug 30, 2021

Commits on Sep 5, 2021

Fix a subtle bug in Decimal.ulp and adjust tests.
xwu
committed

Commits on Sep 7, 2021

Fix implementation of Decimal.nextUp.
xwu
committed