[FSSDK-10642] Refactor batch event processor #867

Job	Run time
crossbrowser_and_umd_unit_tests	28s
lint	30s
unit_tests (16)	30s
unit_tests (18)	31s
unit_tests (20)	28s
unit_tests (22)	31s
integration_tests / test	7s
fullstack_production_suite / test	3s
lint_markdown_files / lint	53s
Coveralls coverage	0s
	4m 1s

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