feat(rpc): gettxchainlocks should return mempool=false when tx not in mempool (#5742)

## Issue being fixed or feature implemented
Platform (in the scope of Withdrawals) need to be aware if a tx isn't in
mempool when requesting status of a tx using RPC `gettxchainlocks`.
cc @markin-io

## What was done?

- mempool is passed to `GetTransaction` and saving the result for
checking latter.
- If the returned tx_ref is nullptr, then the RPC returns null for the
corresponding tx in the array.

Example: 
`tx1` is mined and chainlocked, `tx2` is in mempool and `tx3` doesn't
exist.
The result now is:
`[
  {
    "height": 830,
    "chainlock": false,
    "mempool": true
  },
  {
    "height": -1,
    "chainlock": false,
    "mempool": true
  },
  {
    "height": -1,
    "chainlock": false,
    "mempool": false
  }
]`

## How Has This Been Tested?


## Breaking Changes


## Checklist:
- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have added or updated relevant unit/integration/functional/e2e
tests
- [ ] I have made corresponding changes to the documentation
- [x] I have assigned this pull request to a milestone _(for repository
code-owners and collaborators only)_

---------

Co-authored-by: Konstantin Akimov <knstqq@gmail.com>
Co-authored-by: UdjinM6 <UdjinM6@users.noreply.github.com>

doc/release-notes-5742.md

@@ -0,0 +1,4 @@
+RPC changes
+-----------
+
+RPC `gettxchainlocks` will also return the status `mempool` indicating wether the transaction is in the mempool or not.

src/rpc/rawtransaction.cpp

@@ -269,7 +269,7 @@ static UniValue gettxchainlocks(const JSONRPCRequest& request)
 {
     RPCHelpMan{
         "gettxchainlocks",
-        "\nReturns the block height each transaction was mined at and whether it is chainlocked or not.\n",
+        "\nReturns the block height at which each transaction was mined, and indicates whether it is in the mempool, chainlocked, or neither.\n",
         {
             {"txids", RPCArg::Type::ARR, RPCArg::Optional::NO, "The transaction ids (no more than 100)",
                 {
@@ -284,6 +284,7 @@ static UniValue gettxchainlocks(const JSONRPCRequest& request)
                 {
                     {RPCResult::Type::NUM, "height", "The block height"},
                     {RPCResult::Type::BOOL, "chainlock", "Chainlock status for the block containing the transaction"},
+                    {RPCResult::Type::BOOL, "mempool", "Mempool status for the transaction"},
                 }},
             }
         },
@@ -320,7 +321,15 @@ static UniValue gettxchainlocks(const JSONRPCRequest& request)
         int height{-1};
         bool chainLock{false};
 
-        GetTransaction(nullptr, nullptr, txid, Params().GetConsensus(), hash_block);
+        const auto tx_ref = GetTransaction(nullptr, node.mempool.get(), txid, Params().GetConsensus(), hash_block);
+
+        if (tx_ref == nullptr) {
+            result.pushKV("height", -1);
+            result.pushKV("chainlock", false);
+            result.pushKV("mempool", false);
+            result_arr.push_back(result);
+            continue;
+        }
 
         if (!hash_block.IsNull()) {
             LOCK(cs_main);
@@ -334,6 +343,7 @@ static UniValue gettxchainlocks(const JSONRPCRequest& request)
         }
         result.pushKV("height", height);
         result.pushKV("chainlock", chainLock);
+        result.pushKV("mempool", height == -1);
         result_arr.push_back(result);
     }
     return result_arr;

test/functional/rpc_verifychainlock.py

@@ -22,6 +22,9 @@ class RPCVerifyChainLockTest(DashTestFramework):
         self.set_dash_test_params(5, 3, [["-whitelist=127.0.0.1"], [], [], [], []], fast_dip3_enforcement=True)
         self.set_dash_llmq_test_params(3, 2)
 
+    def cl_helper(self, height, chainlock, mempool):
+        return {'height': height, 'chainlock': chainlock, 'mempool': mempool}
+
     def run_test(self):
         node0 = self.nodes[0]
         node1 = self.nodes[1]
@@ -63,12 +66,12 @@ class RPCVerifyChainLockTest(DashTestFramework):
         height1 = node1.getblockcount()
         tx0 = node0.getblock(node0.getbestblockhash())['tx'][0]
         tx1 = node1.getblock(node1.getbestblockhash())['tx'][0]
-        locks0 = node0.gettxchainlocks([tx0, tx1])
-        locks1 = node1.gettxchainlocks([tx0, tx1])
-        unknown_cl_helper = {'height': -1, 'chainlock': False}
-        assert_equal(locks0, [{'height': height, 'chainlock': True}, unknown_cl_helper])
-        assert_equal(locks1, [unknown_cl_helper, {'height': height1, 'chainlock': False}])
-
+        tx2 = node0.sendtoaddress(node0.getnewaddress(), 1)
+        locks0 = node0.gettxchainlocks([tx0, tx1, tx2])
+        locks1 = node1.gettxchainlocks([tx0, tx1, tx2])
+        unknown_cl_helper = self.cl_helper(-1, False, False)
+        assert_equal(locks0, [self.cl_helper(height, True, False), unknown_cl_helper, self.cl_helper(-1, False, True)])
+        assert_equal(locks1, [unknown_cl_helper, self.cl_helper(height1, False, False), unknown_cl_helper])
 
 if __name__ == '__main__':
     RPCVerifyChainLockTest().main()