kernel: Move kernel-specific cache size options to kernel

Carrying non-kernel related fields in the cache sizes for the indexes is
confusing for kernel library users. The cache sizes also are set
currently with magic numbers in bitcoin-chainstate. The comments for the
cache size calculations are also not completely clear.

Solve these things by moving the kernel-specific cache size fields to
their own struct.

This slightly changes the way the cache is allocated if the txindex
and/or blockfilterindex is used. Since they are now given precedence
over the block tree db cache, this results in a bit less cache being
allocated to the block tree db, coinsdb and coins caches. The effect is
negligible though, i.e. cache sizes with default dbcache reported
through the logs are:

master:
Cache configuration:
* Using 2.0 MiB for block index database
* Using 56.0 MiB for transaction index database
* Using 49.0 MiB for basic block filter index database
* Using 8.0 MiB for chain state database
* Using 335.0 MiB for in-memory UTXO set (plus up to 286.1 MiB of unused mempool space)

this branch:
Cache configuration:
* Using 2.0 MiB for block index database
* Using 56.2 MiB for transaction index database
* Using 49.2 MiB for basic block filter index database
* Using 8.0 MiB for chain state database
* Using 334.5 MiB for in-memory UTXO set (plus up to 286.1 MiB of unused mempool space)

src/node/chainstate.cpp

@@ -8,9 +8,9 @@
 #include <chain.h>
 #include <coins.h>
 #include <consensus/params.h>
+#include <kernel/caches.h>
 #include <logging.h>
 #include <node/blockstorage.h>
-#include <node/caches.h>
 #include <sync.h>
 #include <threadsafety.h>
 #include <tinyformat.h>
@@ -29,6 +29,8 @@
 #include <memory>
 #include <vector>
 
+using kernel::CacheSizes;
+
 namespace node {
 // Complete initialization of chainstates after the initial call has been made
 // to ChainstateManager::InitializeChainstate().