fa6ab8ada1 rpc: Return more specific reject reason for submitblock (MarcoFalke)
Pull request description:
The second commit in #13439 made the `TODO` in the first commit impossible to solve.
The meaning of `fNewBlock` changed from "This is the first time we process this block" to "We are about to write the new *valid* block".
So whenever `fNewBlock` is true, the block was valid. And whenever the `fNewBlock` is false, the block is either valid or invalid. If it was valid and not new, we know it is a `"duplicate"`. In all other cases, the `BIP22ValidationResult()` will return the reason why it is invalid.
Tree-SHA512: 4b6edf7a912339c3acb0fccfabbdd6d812a0321fb1639c244c2714e58dc119aa2b8c6bf8f7d61ea609a1b861bbc23f920370fcf989c48452721e259a8ce93d24
