perf: use `shallowRef` server-side for `datetimeFormats`#2333

kazupon merged 1 commit intointlify:masterintlify/vue-i18n:masterfrom

BobbieGoede:perf/date-tome-formats-shallow-refBobbieGoede/vue-i18n-next:perf/date-tome-formats-shallow-refCopy head branch name to clipboard