[FSSDK-10642] Refactor batch event processor #866

Job	Run time
crossbrowser_and_umd_unit_tests	37s
lint	27s
unit_tests (16)	31s
unit_tests (18)	32s
unit_tests (20)	26s
unit_tests (22)	29s
fullstack_production_suite / test	7s
integration_tests / test	4s
lint_markdown_files / lint	1m 3s
Coveralls coverage	0s
	4m 16s

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