Make inner classes static when feasible (on main)

A static nested class does not keep an implicit reference to its
enclosing instance.

This prevents a common cause of memory leaks and uses less memory per
instance of the class.

Closes gh-28433

spring-beans/src/main/java/org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessor.java

@@ -654,7 +654,7 @@ public class AutowiredAnnotationBeanPostProcessor implements SmartInstantiationA
 	/**
 	 * Base class representing injection information.
 	 */
-	private abstract class AutowiredElement extends InjectionMetadata.InjectedElement {
+	private abstract static class AutowiredElement extends InjectionMetadata.InjectedElement {
 
 		protected final boolean required;
 

spring-beans/src/main/java/org/springframework/beans/factory/aot/BeanDefinitionPropertyValueCodeGenerator.java

@@ -119,7 +119,7 @@ class BeanDefinitionPropertyValueCodeGenerator {
 	/**
 	 * {@link Delegate} for {@code primitive} types.
 	 */
-	private class PrimitiveDelegate implements Delegate {
+	private static class PrimitiveDelegate implements Delegate {
 
 		private static final Map<Character, String> CHAR_ESCAPES;
 
@@ -177,7 +177,7 @@ class BeanDefinitionPropertyValueCodeGenerator {
 	/**
 	 * {@link Delegate} for {@link String} types.
 	 */
-	private class StringDelegate implements Delegate {
+	private static class StringDelegate implements Delegate {
 
 		@Override
 		@Nullable
@@ -194,7 +194,7 @@ class BeanDefinitionPropertyValueCodeGenerator {
 	/**
 	 * {@link Delegate} for {@link Enum} types.
 	 */
-	private class EnumDelegate implements Delegate {
+	private static class EnumDelegate implements Delegate {
 
 		@Override
 		@Nullable
@@ -212,7 +212,7 @@ class BeanDefinitionPropertyValueCodeGenerator {
 	/**
 	 * {@link Delegate} for {@link Class} types.
 	 */
-	private class ClassDelegate implements Delegate {
+	private static class ClassDelegate implements Delegate {
 
 		@Override
 		@Nullable
@@ -229,7 +229,7 @@ class BeanDefinitionPropertyValueCodeGenerator {
 	/**
 	 * {@link Delegate} for {@link ResolvableType} types.
 	 */
-	private class ResolvableTypeDelegate implements Delegate {
+	private static class ResolvableTypeDelegate implements Delegate {
 
 		@Override
 		@Nullable
@@ -512,7 +512,7 @@ class BeanDefinitionPropertyValueCodeGenerator {
 	/**
 	 * {@link Delegate} for {@link BeanReference} types.
 	 */
-	private class BeanReferenceDelegate implements Delegate {
+	private static class BeanReferenceDelegate implements Delegate {
 
 		@Override
 		@Nullable

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassPostProcessor.java

@@ -509,7 +509,7 @@ public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPo
 	}
 
 
-	private class AotContribution implements BeanFactoryInitializationAotContribution {
+	private static class AotContribution implements BeanFactoryInitializationAotContribution {
 
 		private static final String BEAN_FACTORY_VARIABLE = BeanFactoryInitializationCode.BEAN_FACTORY_VARIABLE;