[android][ios][database] Add missing setPriority and setWithPriority methods

lib/modules/database/reference.js

@@ -91,6 +91,29 @@ export default class Reference extends ReferenceBase {
     return promisify('set', FirebaseDatabase)(path, _value);
   }
 
+  /**
+   *
+   * @param priority
+   * @returns {*}
+   */
+  setPriority(priority: string | number | null) {
+    const path = this.path;
+    const _priority = this._serializeAnyType(priority);
+    return promisify('priority', FirebaseDatabase)(path, _priority);
+  }
+
+  /**
+   *
+   * @param priority
+   * @returns {*}
+   */
+  setWithPriority(value: any, priority: string | number | null) {
+    const path = this.path;
+    const _priority = this._serializeAnyType(priority);
+    const _value = this._serializeAnyType(value);
+    return promisify('withPriority', FirebaseDatabase)(path, _value, _priority);
+  }
+
   /**
    *
    * @param val