Pass fee estimator into CTxMempool

This partially reverts commit 7145239.

Author: luke-jr

src/init.cpp

@@ -1545,6 +1545,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     assert(!node.chainman);
 
     CTxMemPool::Options mempool_opts{
+        .estimator = node.fee_estimator.get(),
         .check_ratio = chainparams.DefaultConsistencyChecks() ? 1 : 0,
         .signals = &validation_signals,
     };

src/kernel/mempool_options.h

@@ -13,6 +13,7 @@
 #include <cstdint>
 #include <optional>
 
+class CBlockPolicyEstimator;
 class ValidationSignals;
 
 enum class RBFPolicy { Never, OptIn, Always };
@@ -42,6 +43,8 @@ namespace kernel {
  * Most of the time, this struct should be referenced as CTxMemPool::Options.
  */
 struct MemPoolOptions {
+    /* Used to estimate appropriate transaction fees. */
+    CBlockPolicyEstimator* estimator{nullptr};
     /* The ratio used to determine how often sanity checks will run.  */
     int check_ratio{0};
     int64_t max_size_bytes{DEFAULT_MAX_MEMPOOL_SIZE_MB * 1'000'000};

src/txmempool.h

@@ -209,6 +209,8 @@ struct entry_time {};
 struct ancestor_score {};
 struct index_by_wtxid {};
 
+class CBlockPolicyEstimator;
+
 /**
  * Information about a mempool transaction.
  */