refactor: define new Synchronizer and Initializer interfaces for FDv2 #1748

Job	Run time
build-test-server-curl	7m 26s
contract-tests-curl	4m 24s
build-test-server-mac-curl	5m 46s
contract-tests	4m 12s
build-test-server-windows-curl	18m 8s
build-test-server-mac	5m 27s
build-test-server	7m 33s
build-test-server-windows	17m 52s
	1h 10m 48s

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