[FSSDK-10642] Refactor batch event processor #869

Job	Run time
crossbrowser_and_umd_unit_tests	6h 0m 13s
lint	54s
unit_tests (16)	1m 12s
unit_tests (18)	1m 14s
unit_tests (20)	1m 7s
unit_tests (22)	58s
integration_tests / test	5s
fullstack_production_suite / test	4s
lint_markdown_files / lint	54s
Coveralls coverage	0s
	6h 6m 41s

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