Refactor Wallet import code (#5638)

* Refactor Wallet import code

The code for wallet import was incredibly messy as it evolved over time from various requests.

This PR:
* splits up each supported format into its own file
* Supports taproot descriptors (through a hack until NBitcoin supports it internally) fixes #5518
* Reduces different paths for handling electrum/non-electrum xpubs
* Allows plugins to add their own import support formats for onchain wallets.

* Update NBitcoin to parse tr descriptors

* Fix warnings

* Use dedicated type OnChainWalletParsers

---------

Co-authored-by: nicolas.dorier <nicolas.dorier@gmail.com>

BTCPayServer/Services/WalletFileParsing/ElectrumWalletFileParser.cs

@@ -0,0 +1,88 @@
+#nullable enable
+using System;
+using BTCPayServer;
+using NBitcoin;
+using Newtonsoft.Json.Linq;
+namespace BTCPayServer.Services.WalletFileParsing;
+public class ElectrumWalletFileParser : IWalletFileParser
+{
+    public (BTCPayServer.DerivationSchemeSettings? DerivationSchemeSettings, string? Error) TryParse(BTCPayNetwork network,
+        string data)
+    {
+        try
+        {
+            var derivationSchemeParser = network.GetDerivationSchemeParser();
+            var jobj = JObject.Parse(data);
+            var result = new BTCPayServer.DerivationSchemeSettings() {Network = network};
+
+            if (jobj["keystore"] is JObject keyStore)
+            {
+                result.Source = "ElectrumFile";
+                jobj = keyStore;
+
+                if (!jobj.TryGetValue("xpub", StringComparison.InvariantCultureIgnoreCase, out var xpubToken))
+                {
+                    return (null, "no xpub");
+                }
+                var strategy = derivationSchemeParser.Parse(xpubToken.Value<string>(), false, false, true);
+                result.AccountDerivation = strategy;
+                result.AccountOriginal = xpubToken.Value<string>();
+                result.GetSigningAccountKeySettings();
+                
+                if (jobj["label"]?.Value<string>() is string label)
+                {
+                    try
+                    {
+                        result.Label = label;
+                    }
+                    catch
+                    {
+                        return (null, "Label was not a string");
+                    }
+                }
+
+                if (jobj["ckcc_xfp"]?.Value<uint>() is uint xfp)
+                {
+                    try
+                    {
+                        result.AccountKeySettings[0].RootFingerprint =
+                            new HDFingerprint(xfp);
+                    }
+                    catch
+                    {
+                        return (null, "fingerprint was not a uint");
+                    }
+                }
+
+                if (jobj["derivation"]?.Value<string>() is string derivation)
+                {
+                    try
+                    {
+                        result.AccountKeySettings[0].AccountKeyPath = new KeyPath(derivation);
+                    }
+                    catch
+                    {
+                        return (null, "derivation keypath was not valid");
+                    }
+                }
+                
+                
+                if (jobj.ContainsKey("ColdCardFirmwareVersion"))
+                {
+                    result.Source = "ColdCard";
+                }
+                else if (jobj.ContainsKey("CoboVaultFirmwareVersion"))
+                {
+                    result.Source = "CoboVault";
+                }
+                return (result, null);
+            }
+
+        }
+        catch (FormatException)
+        {
+            return (null, "invalid xpub");
+        }
+        return (null, null);
+    }
+}