Add with_fset fns to datetime types (#5942) #2621

Job	Run time
Check Credentials for jobs that need JSON credentials	2s
WASM Demo	1m 32s
bench-binsize	2m 28s
bench-memory (macos-latest)	3m 21s
bench-memory (ubuntu-latest)	3m 27s
bench-memory (windows-latest)	9m 20s
bench-perf (components/collections)	4m 40s
bench-perf (components/datetime)	2m 27s
bench-perf (components/locale)	2m 40s
bench-perf (components/locale_core)	5m 24s
bench-perf (components/plurals)	6m 12s
bench-perf (components/segmenter)	3m 50s
bench-perf (provider/blob)	2m 31s
bench-perf (utils/fixed_decimal)	5m 51s
bench-perf (utils/litemap)	2m 8s
bench-perf (utils/tinystr)	6m 36s
bench-perf (utils/writeable)	4m 3s
bench-perf (utils/zerotrie)	5m 22s
bench-perf (utils/zerovec)	8m 36s
Rust docs	4m 27s
Dart docs	1m 32s
C++ docs	42s
TypeScript docs	41s
Deploy to GitHub Pages	7m 25s
	1h 35m 17s

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