Backend: electrumServer's IdFromPos support (#205)

This is used for our RgsToElectrumServerMiddleware code, see:
nblockchain/rapid-gossip-sync-server#1

src/GWallet.Backend/UtxoCoin/ElectrumClient.fs

@@ -83,6 +83,13 @@ module ElectrumClient =
         return blockchainTransactionResult.Result
     }
 
+    // DON'T DELETE, used in external projects
+    let GetBlockchainTransactionIdFromPos (height: UInt32) (txPos: UInt32) (stratumServer: Async<StratumClient>) = async {
+        let! stratumClient = stratumServer
+        let! blockchainTransactionResult = stratumClient.BlockchainTransactionIdFromPos height txPos
+        return blockchainTransactionResult.Result
+    }
+
     let EstimateFee (numBlocksTarget: int) (stratumServer: Async<StratumClient>): Async<decimal> = async {
         let! stratumClient = stratumServer
         let! estimateFeeResult = stratumClient.BlockchainEstimateFee numBlocksTarget

src/GWallet.Backend/UtxoCoin/StratumClient.fs

@@ -51,6 +51,13 @@ type BlockchainTransactionGetResult =
         Result: string;
     }
 
+// DON'T DELETE, used in external projects
+type BlockchainTransactionIdFromPosResult =
+    {
+        Id: int
+        Result: string
+    }
+
 type BlockchainEstimateFeeResult =
     {
         Id: int;
@@ -258,6 +265,19 @@ type StratumClient (jsonRpcClient: JsonRpcTcpClient) =
             return resObj
         }
 
+    // DON'T DELETE, used in external projects
+    member self.BlockchainTransactionIdFromPos height txPos: Async<BlockchainTransactionIdFromPosResult> =
+        let obj = {
+            Id = 0;
+            Method = "blockchain.transaction.id_from_pos";
+            Params = [height :> obj; txPos :> obj]
+        }
+        let json = Serialize obj
+        async {
+            let! resObj,_ = self.Request<BlockchainTransactionIdFromPosResult> json
+            return resObj
+        }
+
     // NOTE: despite Electrum-X official docs claiming that this method is deprecated... it's not! go read the official
     //       non-shitcoin forked version of the docs: https://electrumx-spesmilo.readthedocs.io/en/latest/protocol-methods.html#blockchain-estimatefee
     member self.BlockchainEstimateFee (numBlocksTarget: int): Async<BlockchainEstimateFeeResult> =