Revise changes to DefaultGenerationContext and GeneratedClasses

In order to reduce the surface area of published APIs in the affected
classes, this commit:

- Reverts the changes made to GeneratedClasses in c354b1014d.

- Reverts the changes made to DefaultGenerationContext in a28ec3a0a8.

- Makes the DefaultGenerationContext(DefaultGenerationContext, String)
  constructor protected.

- Reworks the internals of TestContextGenerationContext to align with
  the above changes.

See gh-30861
Closes gh-30895
Closes gh-30897

spring-core/src/main/java/org/springframework/aot/generate/DefaultGenerationContext.java

@@ -78,7 +78,7 @@ public class DefaultGenerationContext implements GenerationContext {
 	 * @param generatedFiles the generated files
 	 * @param runtimeHints the runtime hints
 	 */
-	protected DefaultGenerationContext(GeneratedClasses generatedClasses,
+	DefaultGenerationContext(GeneratedClasses generatedClasses,
 			GeneratedFiles generatedFiles, RuntimeHints runtimeHints) {
 
 		Assert.notNull(generatedClasses, "'generatedClasses' must not be null");
@@ -90,9 +90,18 @@ public class DefaultGenerationContext implements GenerationContext {
 		this.runtimeHints = runtimeHints;
 	}
 
-	private DefaultGenerationContext(DefaultGenerationContext existing, String name) {
-		int sequence = existing.sequenceGenerator.computeIfAbsent(name, key -> new AtomicInteger()).getAndIncrement();
-		String featureName = (sequence > 0 ? name + sequence : name);
+	/**
+	 * Create a new {@link DefaultGenerationContext} instance based on the
+	 * supplied {@code existing} context and feature name.
+	 * @param existing the existing context upon which to base the new one
+	 * @param featureName the feature name to use
+	 * @since 6.0.12
+	 */
+	protected DefaultGenerationContext(DefaultGenerationContext existing, String featureName) {
+		int sequence = existing.sequenceGenerator.computeIfAbsent(featureName, key -> new AtomicInteger()).getAndIncrement();
+		if (sequence > 0) {
+			featureName += sequence;
+		}
 		this.sequenceGenerator = existing.sequenceGenerator;
 		this.generatedClasses = existing.generatedClasses.withFeatureNamePrefix(featureName);
 		this.generatedFiles = existing.generatedFiles;

spring-core/src/main/java/org/springframework/aot/generate/GeneratedClasses.java

@@ -176,19 +176,6 @@ public class GeneratedClasses {
 		return addForFeatureComponent(featureName, ClassName.get(targetComponent), type);
 	}
 
-	/**
-	 * Create a new {@link GeneratedClasses} instance using the specified feature
-	 * name prefix to qualify generated class names for a dedicated round of code
-	 * generation.
-	 * @param featureNamePrefix the feature name prefix to use
-	 * @return a new instance for the specified feature name prefix
-	 * @since 6.0.12
-	 */
-	public GeneratedClasses withFeatureNamePrefix(String featureNamePrefix) {
-		return new GeneratedClasses(this.classNameGenerator.withFeatureNamePrefix(featureNamePrefix),
-				this.classes, this.classesByOwner);
-	}
-
 	private GeneratedClass createAndAddGeneratedClass(String featureName,
 			@Nullable ClassName targetComponent, Consumer<TypeSpec.Builder> type) {
 
@@ -212,6 +199,18 @@ public class GeneratedClasses {
 		}
 	}
 
+	/**
+	 * Create a new {@link GeneratedClasses} instance using the specified feature
+	 * name prefix to qualify generated class names for a dedicated round of code
+	 * generation.
+	 * @param featureNamePrefix the feature name prefix to use
+	 * @return a new instance for the specified feature name prefix
+	 */
+	GeneratedClasses withFeatureNamePrefix(String featureNamePrefix) {
+		return new GeneratedClasses(this.classNameGenerator.withFeatureNamePrefix(featureNamePrefix),
+				this.classes, this.classesByOwner);
+	}
+
 	private record Owner(String featureNamePrefix, String featureName, @Nullable ClassName target) {
 	}