Modernization and cleanup of job state related client code. #25285

Job	Run time
build-client / build-client	11m 7s
setup-selenium / setup_chromedriver	3s
Test (3.8, 0)	43m 38s
Test (3.8, 1)	53m 26s
Test (3.8, 2)	48m 52s
	2h 37m 6s

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