docs(common/):add comments for complex funcs #3780

Job	Run time
Basic Checks	1m 54s
Unit Tests	24m 5s
Integration Tests (raft)	11m 48s
Integration Tests (pvtdata)	11m 45s
Integration Tests (pvtdatapurge e2e)	10m 59s
Integration Tests (ledger)	13m 29s
Integration Tests (lifecycle)	7m 2s
Integration Tests (smartbft)	20m 24s
Integration Tests (discovery gossip devmode pluggable)	7m 47s
Integration Tests (gateway idemix pkcs11 configtx configtxlator)	17m 28s
Integration Tests (sbe nwo msp)	8m 59s
	2h 15m 40s

Provide feedback