Implement refactor to utilize new donation configuration endpoint.

core-util/src/main/java/org/signal/core/util/money/PlatformCurrencyUtil.kt

@@ -0,0 +1,24 @@
+package org.signal.core.util.money
+
+import java.util.Currency
+
+/**
+ * Utility methods for java.util.Currency
+ *
+ * This is prefixed with "Platform" as there are several different Currency classes
+ * available in the app, and this utility class is specifically for dealing with
+ * java.util.Currency
+ */
+object PlatformCurrencyUtil {
+
+  val USD: Currency = Currency.getInstance("USD")
+
+  /**
+   * Note: Adding this as an extension method of Currency causes some confusion in
+   *       AndroidStudio due to a separate Currency class from the AndroidSDK having
+   *       an extension method of the same signature.
+   */
+  fun getAvailableCurrencyCodes(): Set<String> {
+    return Currency.getAvailableCurrencies().map { it.currencyCode }.toSet()
+  }
+}