[FSSDK-10642] Refactor batch event processor (#960) #884

Job	Run time
crossbrowser_and_umd_unit_tests	6h 0m 13s
lint	3m 36s
unit_tests (16)	1m 23s
unit_tests (18)	1m 23s
unit_tests (20)	1m 21s
unit_tests (22)	1m 6s
fullstack_production_suite / test	3s
integration_tests / test	4s
lint_markdown_files / lint	45s
Coveralls coverage	0s
	6h 9m 54s

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