Merge #17564: rpc: Use mempool from node context instead of global

fa8e650b52 rest: Use mempool from node context instead of global (MarcoFalke)
fa660d65d7 node: Use mempool from node context instead of global (MarcoFalke)
facbaf092f rpc: Use mempool from node context instead of global (MarcoFalke)

Pull request description:

  Currently they are identical, but in the future we might want to turn
  the mempool into a unique_ptr. Replacing the global with the mempool
  pointer from the node context simplifies this step.

ACKs for top commit:
  jnewbery:
    Code review ACK fa8e650b5
  ryanofsky:
    Code review ACK fa8e650b52, Only the discussed REST server changes since the last review.

Tree-SHA512: 0836f3f39cf90306455962918446e5f8612e88c32072b92afc30929aea1f17430bbda0e2b3668d36c9d6b97d63a93cf4903185194571108642b7bf5a39b89125

src/interfaces/chain.cpp

@@ -263,7 +263,7 @@ public:
         }
         return true;
     }
-    void findCoins(std::map<COutPoint, Coin>& coins) override { return FindCoins(coins); }
+    void findCoins(std::map<COutPoint, Coin>& coins) override { return FindCoins(m_node, coins); }
     double guessVerificationProgress(const uint256& block_hash) override
     {
         LOCK(cs_main);

src/interfaces/node.cpp

@@ -167,8 +167,8 @@ public:
     }
     int64_t getTotalBytesRecv() override { return m_context.connman ? m_context.connman->GetTotalBytesRecv() : 0; }
     int64_t getTotalBytesSent() override { return m_context.connman ? m_context.connman->GetTotalBytesSent() : 0; }
-    size_t getMempoolSize() override { return ::mempool.size(); }
-    size_t getMempoolDynamicUsage() override { return ::mempool.DynamicMemoryUsage(); }
+    size_t getMempoolSize() override { return m_context.mempool ? m_context.mempool->size() : 0; }
+    size_t getMempoolDynamicUsage() override { return m_context.mempool ? m_context.mempool->DynamicMemoryUsage() : 0; }
     bool getHeaderTip(int& height, int64_t& block_time) override
     {
         LOCK(::cs_main);