[ci skip] Add defaultId to RegistrarBuilder (#474)

* Add defaultId to RegistrarBuilder

* Make the default key an registrar option

---------

Co-authored-by: shedaniel <daniel@shedaniel.me>

common/src/main/java/dev/architectury/registry/registries/options/DefaultIdRegistrarOption.java

@@ -0,0 +1,25 @@
+/*
+ * This file is part of architectury.
+ * Copyright (C) 2020, 2021, 2022 architectury
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+package dev.architectury.registry.registries.options;
+
+import net.minecraft.resources.ResourceLocation;
+
+public record DefaultIdRegistrarOption(ResourceLocation defaultId) implements RegistrarOption {
+}