Add RegistryAccess for managing registries

paper-api/src/test/java/io/papermc/paper/registry/TestRegistryAccess.java

@@ -0,0 +1,20 @@
+package io.papermc.paper.registry;
+
+import org.bukkit.Keyed;
+import org.bukkit.Registry;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class TestRegistryAccess implements RegistryAccess {
+
+    @Override
+    @Deprecated(since = "1.20.6", forRemoval = true)
+    public @Nullable <T extends Keyed> Registry<T> getRegistry(final @NotNull Class<T> type) {
+        throw new UnsupportedOperationException("Not supported");
+    }
+
+    @Override
+    public @NotNull <T extends Keyed> Registry<T> getRegistry(final @NotNull RegistryKey<T> registryKey) {
+        throw new UnsupportedOperationException("Not supported");
+    }
+}