move-only: Move CBlockTreeDB to node/blockstorage

The block index (CBlockTreeDB) is required to write and read blocks, so
move it to blockstorage. This allows to drop the txdb.h include from
`node/blockstorage.h`.

Can be reviewed with:

--color-moved=dimmed-zebra  --color-moved-ws=ignore-all-space

src/node/blockstorage.h

@@ -7,17 +7,25 @@
 
 #include <attributes.h>
 #include <chain.h>
+#include <dbwrapper.h>
 #include <kernel/blockmanager_opts.h>
 #include <kernel/chainparams.h>
 #include <kernel/cs_main.h>
 #include <protocol.h>
 #include <sync.h>
-#include <txdb.h>
 #include <util/fs.h>
+#include <util/hasher.h>
 
 #include <atomic>
 #include <cstdint>
+#include <functional>
+#include <limits>
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
 #include <unordered_map>
+#include <utility>
 #include <vector>
 
 class BlockValidationState;
@@ -36,7 +44,26 @@ namespace util {
 class SignalInterrupt;
 } // namespace util
 
+namespace kernel {
+/** Access to the block database (blocks/index/) */
+class CBlockTreeDB : public CDBWrapper
+{
+public:
+    using CDBWrapper::CDBWrapper;
+    bool WriteBatchSync(const std::vector<std::pair<int, const CBlockFileInfo*>>& fileInfo, int nLastFile, const std::vector<const CBlockIndex*>& blockinfo);
+    bool ReadBlockFileInfo(int nFile, CBlockFileInfo& info);
+    bool ReadLastBlockFile(int& nFile);
+    bool WriteReindexing(bool fReindexing);
+    void ReadReindexing(bool& fReindexing);
+    bool WriteFlag(const std::string& name, bool fValue);
+    bool ReadFlag(const std::string& name, bool& fValue);
+    bool LoadBlockIndexGuts(const Consensus::Params& consensusParams, std::function<CBlockIndex*(const uint256&)> insertBlockIndex, const util::SignalInterrupt& interrupt)
+        EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+};
+} // namespace kernel
+
 namespace node {
+using kernel::CBlockTreeDB;
 
 /** The pre-allocation chunk size for blk?????.dat files (since 0.8) */
 static const unsigned int BLOCKFILE_CHUNK_SIZE = 0x1000000; // 16 MiB