move-only: Move CBlockFileInfo to kernel namespace

Also, move it to the blockstorage module, because it is only used inside
that module.

Can be reviewed with the git option --color-moved=dimmed-zebra

src/node/blockstorage.cpp

@@ -35,6 +35,7 @@
 #include <util/signalinterrupt.h>
 #include <util/strencodings.h>
 #include <util/syserror.h>
+#include <util/time.h>
 #include <util/translation.h>
 #include <validation.h>
 
@@ -151,6 +152,11 @@ bool BlockTreeDB::LoadBlockIndexGuts(const Consensus::Params& consensusParams, s
 
     return true;
 }
+
+std::string CBlockFileInfo::ToString() const
+{
+    return strprintf("CBlockFileInfo(blocks=%u, size=%u, heights=%u...%u, time=%s...%s)", nBlocks, nSize, nHeightFirst, nHeightLast, FormatISO8601Date(nTimeFirst), FormatISO8601Date(nTimeLast));
+}
 } // namespace kernel
 
 namespace node {