move-only: add node/mining_types.h

Move mining related structs there.

This simplifies includes in later commits and makes the code easier to
understand for Mining IPC client developers.

src/interfaces/mining.h

@@ -8,6 +8,7 @@
 #include <consensus/amount.h>
 #include <interfaces/types.h>
 #include <node/types.h>
+#include <node/mining_types.h>
 #include <primitives/block.h>
 #include <primitives/transaction.h>
 #include <uint256.h>
@@ -22,9 +23,6 @@ namespace node {
 struct NodeContext;
 } // namespace node
 
-class BlockValidationState;
-class CScript;
-
 namespace interfaces {
 
 //! Block template interface