Create Dart snippets and reference them

Co-Authored-By: ok300 <106775972+ok300@users.noreply.github.com>

snippets/dart_snippets/lib/lnurl_withdraw.dart

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+import 'package:breez_sdk/breez_sdk.dart';
+import 'package:breez_sdk/bridge_generated.dart';
+
+Future<void> lnurlWithdraw() async {
+  // ANCHOR: lnurl-withdraw
+  /// Endpoint can also be of the form:
+  /// lnurlw://domain.com/lnurl-withdraw?key=val
+  String lnurlWithdrawUrl =
+      "lnurl1dp68gurn8ghj7mr0vdskc6r0wd6z7mrww4exctthd96xserjv9mn7um9wdekjmmw843xxwpexdnxzen9vgunsvfexq6rvdecx93rgdmyxcuxverrvcursenpxvukzv3c8qunsdecx33nzwpnvg6ryc3hv93nzvecxgcxgwp3h33lxk";
+
+  InputType inputType = await BreezSDK().parseInput(input: lnurlWithdrawUrl);
+  if (inputType is InputType_LnUrlWithdraw) {
+    int amountMsat = inputType.data.minWithdrawable;
+    LnUrlWithdrawRequest req = LnUrlWithdrawRequest(
+      data: inputType.data,
+      amountMsat: amountMsat,
+      description: "<description>",
+    );
+    LnUrlWithdrawResult result = await BreezSDK().lnurlWithdraw(req: req);
+    print(result.data);
+  }
+  // ANCHOR_END: lnurl-withdraw
+}