Create Dart snippets and reference them

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

snippets/dart_snippets/lib/fiat_currencies.dart

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+import 'package:breez_sdk/breez_sdk.dart';
+import 'package:breez_sdk/bridge_generated.dart';
+
+Future<List<FiatCurrency>> listFiatCurrencies() async {
+  // ANCHOR: list-fiat-currencies
+  List<FiatCurrency> fiatCurrencyList = await BreezSDK().listFiatCurrencies();
+  // ANCHOR_END: list-fiat-currencies
+  return fiatCurrencyList;
+}
+
+Future<Map<String, Rate>> fetchFiatRates(String lspId) async {
+  // ANCHOR: fetch-fiat-rates
+  Map<String, Rate> fiatRatesMap = await BreezSDK().fetchFiatRates();
+  // print your desired rate
+  print(fiatRatesMap["USD"]?.value);
+  // ANCHOR_END: fetch-fiat-rates
+  return fiatRatesMap;
+}
+
+Future<Map<FiatCurrency, Rate>> fiatCurrenciesAndRate() async {
+  // ANCHOR: get-fiat-currencies-and-rates
+  List<FiatCurrency> fiatCurrencies = await BreezSDK().listFiatCurrencies();
+  Map<String, Rate> fiatRates = await BreezSDK().fetchFiatRates();
+
+  var sorted = fiatCurrencies.toList();
+  sorted.sort((f1, f2) {
+    return f1.id.compareTo(f2.id);
+  });
+
+  Map<FiatCurrency, Rate> result = {};
+  for (var currency in sorted) {
+    var rate = fiatRates[currency.id];
+    if (rate != null) {
+      result[currency] = rate;
+    }
+  }
+
+  return result;
+  // ANCHOR_END: get-fiat-currencies-and-rates
+}