Revert exposing `getModulePrefix()` on `RepositoryConfigurationExtension`.

This is a breaking change as many modules implement a protected method. We're going to change this later with #2644.

Original pull request: #2635.
See #2634.

src/main/java/org/springframework/data/repository/config/RepositoryBeanDefinitionBuilder.java

@@ -170,7 +170,7 @@ class RepositoryBeanDefinitionBuilder {
 		fragmentsBuilder.addConstructorArgValue(fragmentBeanNames);
 
 		String fragmentsBeanName = BeanDefinitionReaderUtils
-				.uniqueBeanName(String.format("%s.%s.fragments", extension.getModulePrefix(),
+				.uniqueBeanName(String.format("%s.%s.fragments", extension.getModuleName().toLowerCase(Locale.ROOT),
 						ClassUtils.getShortName(configuration.getRepositoryInterface())), registry);
 		registry.registerBeanDefinition(fragmentsBeanName, fragmentsBuilder.getBeanDefinition());
 		return fragmentsBeanName;

src/main/java/org/springframework/data/repository/config/RepositoryConfigurationExtension.java

@@ -15,15 +15,12 @@
  */
 package org.springframework.data.repository.config;
 
-import java.lang.annotation.Annotation;
 import java.util.Collection;
-import java.util.Collections;
 
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.core.io.ResourceLoader;
-import org.springframework.util.StringUtils;
 
 /**
  * SPI to implement store specific extension to the repository bean definition registration process.
@@ -39,18 +36,7 @@ public interface RepositoryConfigurationExtension {
 	 *
 	 * @return
 	 */
-	default String getModuleName() {
-		return StringUtils.capitalize(getModulePrefix());
-	}
-
-	/**
-	 * Returns the prefix of the module to be used to create the default location for Spring Data named queries and module
-	 * specific bean definitions.
-	 *
-	 * @return must not be {@literal null}.
-	 * @since 3.0
-	 */
-	String getModulePrefix();
+	String getModuleName();
 
 	/**
 	 * Returns all {@link RepositoryConfiguration}s obtained through the given {@link RepositoryConfigurationSource}.

src/main/java/org/springframework/data/repository/config/RepositoryConfigurationExtensionSupport.java

@@ -60,6 +60,11 @@ public abstract class RepositoryConfigurationExtensionSupport implements Reposit
 
 	private boolean noMultiStoreSupport = false;
 
+	@Override
+	public String getModuleName() {
+		return StringUtils.capitalize(getModulePrefix());
+	}
+
 	public <T extends RepositoryConfigurationSource> Collection<RepositoryConfiguration<T>> getRepositoryConfigurations(
 			T configSource, ResourceLoader loader) {
 		return getRepositoryConfigurations(configSource, loader, false);
@@ -104,6 +109,13 @@ public abstract class RepositoryConfigurationExtensionSupport implements Reposit
 	public void registerBeansForRoot(BeanDefinitionRegistry registry,
 			RepositoryConfigurationSource configurationSource) {}
 
+	/**
+	 * Returns the prefix of the module to be used to create the default location for Spring Data named queries.
+	 *
+	 * @return must not be {@literal null}.
+	 */
+	protected abstract String getModulePrefix();
+
 	public void postProcess(BeanDefinitionBuilder builder, RepositoryConfigurationSource source) {}
 
 	public void postProcess(BeanDefinitionBuilder builder, AnnotationRepositoryConfigurationSource config) {}