message: Expose txinwitness for coinbase in JSON form
  txinwitness is used as the witness commitment nonce so is necessary if
  reconstructing block data from RPC data.
diff: @@ -199,6 +199,7 @@ void TxToUniv(const CTransaction& tx, const uint256& hashBlock, UniValue& entry,
  o.pushKV("asm", ScriptToAsmStr(txin.scriptSig, true));
  o.pushKV("hex", HexStr(txin.scriptSig.begin(), txin.scriptSig.end()));
  in.pushKV("scriptSig", o);
  + }
  if (!tx.vin[i].scriptWitness.IsNull()) {
  UniValue txinwitness(UniValue::VARR);
  for (const auto& item : tx.vin[i].scriptWitness.stack) {
  @@ -206,7 +207,6 @@ void TxToUniv(const CTransaction& tx, const uint256& hashBlock, UniValue& entry,
  }
  in.pushKV("txinwitness", txinwitness);
  }
  - }
  in.pushKV("sequence", (int64_t)txin.nSequence);
  vin.push_back(in);
  }
  