Convert CompareInvMempoolOrder to GenTxidVariant

Now that we are storing `CTxMemPool::CompareDepthAndScore` parameters using
`std::variant` we have no portable zero-overhead way of accessing them,
so use `std::visit` and drop `bool wtxid` in-parameter.

Co-authored-by: stickies-v <stickies-v@protonmail.com>

src/node/transaction.cpp

@@ -42,7 +42,7 @@ TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef t
 
     std::promise<void> promise;
     Txid txid = tx->GetHash();
-    uint256 wtxid = tx->GetWitnessHash();
+    Wtxid wtxid = tx->GetWitnessHash();
     bool callback_set = false;
 
     {