Add -blocksxor boolean option

src/kernel/blockmanager_opts.h

@@ -14,12 +14,15 @@ class CChainParams;
 
 namespace kernel {
 
+static constexpr bool DEFAULT_XOR_BLOCKSDIR{true};
+
 /**
  * An options struct for `BlockManager`, more ergonomically referred to as
  * `BlockManager::Options` due to the using-declaration in `BlockManager`.
  */
 struct BlockManagerOpts {
     const CChainParams& chainparams;
+    bool use_xor{DEFAULT_XOR_BLOCKSDIR};
     uint64_t prune_target{0};
     bool fast_prune{false};
     const fs::path blocks_dir;