Unify method visibility of private classes

Apply checkstyle rule to ensure that private and package private
classes do not have unnecessary public methods. Test classes have
also been unified as much as possible to use default scoped
inner-classes.

Closes gh-7316

spring-boot-project/spring-boot-docs/src/test/java/org/springframework/boot/docs/autoconfigure/UserServiceAutoConfigurationTests.java

@@ -70,7 +70,7 @@ class UserServiceAutoConfigurationTests {
 	static class UserConfiguration {
 
 		@Bean
-		public UserService myUserService() {
+		UserService myUserService() {
 			return new UserService("mine");
 		}
 

spring-boot-project/spring-boot-docs/src/test/java/org/springframework/boot/docs/context/embedded/TomcatLegacyCookieProcessorExampleTests.java

@@ -51,12 +51,12 @@ class TomcatLegacyCookieProcessorExampleTests {
 	static class TestConfiguration {
 
 		@Bean
-		public TomcatServletWebServerFactory tomcatFactory() {
+		TomcatServletWebServerFactory tomcatFactory() {
 			return new TomcatServletWebServerFactory(0);
 		}
 
 		@Bean
-		public WebServerFactoryCustomizerBeanPostProcessor postProcessor() {
+		WebServerFactoryCustomizerBeanPostProcessor postProcessor() {
 			return new WebServerFactoryCustomizerBeanPostProcessor();
 		}
 

spring-boot-project/spring-boot-docs/src/test/java/org/springframework/boot/docs/web/client/SampleWebClientConfiguration.java

@@ -43,7 +43,7 @@ class SampleWebClientConfiguration {
 	private static class ExampleController {
 
 		@RequestMapping("/example")
-		public ResponseEntity<String> example() {
+		ResponseEntity<String> example() {
 			return ResponseEntity.ok().location(URI.create("https://other.example.com/example")).body("test");
 		}
 

spring-boot-project/spring-boot-docs/src/test/java/org/springframework/boot/docs/web/client/SampleWebClientTests.java

@@ -56,7 +56,7 @@ class SampleWebClientTests {
 	static class Config {
 
 		@Bean
-		public RestTemplateBuilder restTemplateBuilder() {
+		RestTemplateBuilder restTemplateBuilder() {
 			return new RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
 					.setReadTimeout(Duration.ofSeconds(1));
 		}