Harmonize class visibility

Closes gh-19414

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/HttpEncodingAutoConfiguration.java

@@ -68,7 +68,7 @@ public class HttpEncodingAutoConfiguration {
 		return new LocaleCharsetMappingsCustomizer(this.properties);
 	}
 
-	private static class LocaleCharsetMappingsCustomizer
+	static class LocaleCharsetMappingsCustomizer
 			implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory>, Ordered {
 
 		private final HttpProperties.Encoding properties;

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/error/ErrorMvcAutoConfiguration.java

@@ -252,7 +252,7 @@ public class ErrorMvcAutoConfiguration {
 	/**
 	 * {@link WebServerFactoryCustomizer} that configures the server's error pages.
 	 */
-	private static class ErrorPageCustomizer implements ErrorPageRegistrar, Ordered {
+	static class ErrorPageCustomizer implements ErrorPageRegistrar, Ordered {
 
 		private final ServerProperties properties;