move-only: move coins statistics utils out of RPC

These procedures will later be used in the ChainstateManager to compute
statistics (particularly a content hash) for UTXO sets coming in from
snapshots.

src/node/coinstats.h

@@ -0,0 +1,33 @@
+// Copyright (c) 2010 Satoshi Nakamoto
+// Copyright (c) 2009-2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_NODE_COINSTATS_H
+#define BITCOIN_NODE_COINSTATS_H
+
+#include <amount.h>
+#include <uint256.h>
+
+#include <cstdint>
+
+class CCoinsView;
+
+struct CCoinsStats
+{
+    int nHeight;
+    uint256 hashBlock;
+    uint64_t nTransactions;
+    uint64_t nTransactionOutputs;
+    uint64_t nBogoSize;
+    uint256 hashSerialized;
+    uint64_t nDiskSize;
+    CAmount nTotalAmount;
+
+    CCoinsStats() : nHeight(0), nTransactions(0), nTransactionOutputs(0), nBogoSize(0), nDiskSize(0), nTotalAmount(0) {}
+};
+
+//! Calculate statistics about the unspent transaction output set
+bool GetUTXOStats(CCoinsView* view, CCoinsStats& stats);
+
+#endif // BITCOIN_NODE_COINSTATS_H