Backport PR12151 https://github.com/bitcoin/bitcoin/pull/12151/commits
54dc13b rpc: Fix SoftForkMajorityDesc and SoftForkDesc signatures
343b98c rpc: Specify chain tip instead of chain in GetDifficulty
b9f226b rpc: Remove cs_main lock from blockToJSON and blockHeaderToJSON
Backport PR15932 https://github.com/bitcoin/bitcoin/pull/15932/commits
fab00a5 rpc: Serialize in getblock without cs_main
faea564 rpc: Add lock annotations to block{,header}ToJSON