Add feature to support custom `now_utc` implementations #5025

Job	Run time
check-for-run-condition	1s
check-for-modification	4s
build-wasm / build-wasm (ubuntu-latest)	10m 30s
build-and-test (ubuntu-latest)	6m 14s
build-and-test (macos-latest)	4m 4s
build-and-test (windows-latest)	12m 49s
test-wasm-firefox (ubuntu-latest)	3m 30s
test-wasm (ubuntu-latest)	2m 29s
test-wasm-chrome (ubuntu-latest)	4m 37s
	44m 18s

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