Revert "Lift sealed restriction from AccessTransformersConfiguration"

This reverts commit ec5a418.

I decided it was unnecessary for my use-case, and I don't want to expose
or make extensible public API without reason.

Author: Jonathing

at-gradle/src/main/java/net/minecraftforge/accesstransformers/gradle/AccessTransformersConfiguration.java

@@ -7,10 +7,7 @@
 import org.gradle.api.file.RegularFileProperty;
 
 /// Configuration for individual dependencies to be run through AccessTransformers.
-///
-/// @apiNote This interface is not sealed since it is implemented by Forge Gradle for consumers to set the config file
-/// for the Minecraft dependency. Implementing this interface yourself is still highly discouraged.
-public interface AccessTransformersConfiguration {
+public sealed interface AccessTransformersConfiguration permits AccessTransformersContainer.Options, AccessTransformersConfigurationInternal {
     /// Gets the AccessTransformer configuration to use.
     ///
     /// @return The property for the configuration

at-gradle/src/main/java/net/minecraftforge/accesstransformers/gradle/AccessTransformersConfigurationInternal.java

@@ -13,7 +13,7 @@
 import java.util.List;
 import java.util.Objects;
 
-interface AccessTransformersConfigurationInternal extends AccessTransformersConfiguration, HasPublicType {
+non-sealed interface AccessTransformersConfigurationInternal extends AccessTransformersConfiguration, HasPublicType {
     String CONFIGS_EXT_PROPERTY = "__accessTransformers_configs";
 
     static boolean has(Object object) {