scripted-diff: Move src/kernel/coinstats to kernel::

Introduces a new kernel:: namespace and move all of src/kernel/coinstats
under it.

In the verify script, lines like:

line="$(grep -n 'namespace node {' -- src/kernel/coinstats.h | tail -n1 | cut -d: -f1)"
sed -i -e "${line}s@namespace node {@namespace kernel {@" -- src/kernel/coinstats.h

Are intended to replace only the last instance of "namespace node" with
"namespace kernel", this is to avoid replacing forward declarations of
things inside the node:: namespace.

-BEGIN VERIFY SCRIPT-
sed -E -i 's@namespace node@namespace kernel@g' -- src/kernel/coinstats.cpp

line="$(grep -n 'namespace node {' -- src/kernel/coinstats.h | tail -n1 | cut -d: -f1)"
sed -i -e "${line}s@namespace node {@namespace kernel {@" -- src/kernel/coinstats.h

line="$(grep -n '// namespace node' -- src/kernel/coinstats.h | tail -n1 | cut -d: -f1)"
sed -i -e "${line}s@// namespace node@// namespace kernel@" -- src/kernel/coinstats.h

things='(CCoinsStats|CoinStatsHashType|GetBogoSize|TxOutSer|ComputeUTXOStats)'
git grep -lE 'node::'"$things" | xargs sed -E -i 's@node::'"$things"'@kernel::\1@g'
sed -E -i 's@'"$things"'@kernel::\1@g' -- src/node/coinstats.cpp src/node/coinstats.h
sed -E -i 's@BlockManager@node::\0@g' -- src/kernel/coinstats.cpp
-END VERIFY SCRIPT-

src/validation.cpp

@@ -63,8 +63,8 @@ using node::BlockManager;
 using node::BlockMap;
 using node::CBlockIndexHeightOnlyComparator;
 using node::CBlockIndexWorkComparator;
-using node::CCoinsStats;
-using node::CoinStatsHashType;
+using kernel::CCoinsStats;
+using kernel::CoinStatsHashType;
 using node::fImporting;
 using node::fPruneMode;
 using node::fReindex;