Add feature to support custom `now_utc` implementations #5041

Job	Run time
check-for-run-condition	1s
check-for-modification	3s
build-wasm / build-wasm (ubuntu-latest)	40s
build-and-test (ubuntu-latest)	3m 17s
build-and-test (macos-latest)	1m 4s
build-and-test (windows-latest)	10m 39s
test-wasm	0s
test-wasm-chrome	0s
test-wasm-firefox	0s
	15m 44s

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