Stop RequestContextFilter initializing config

Change WebMvcAutoConfigurationAdapter.requestContextFilter() to a static
method so that the configuration class isn't needed when creating it.
This helps to prevent early initialization of beans.

See gh-6178

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/WebMvcAutoConfiguration.java

@@ -195,13 +195,6 @@ public class WebMvcAutoConfiguration {
 			return resolver;
 		}
 
-		@Bean
-		@ConditionalOnMissingBean({ RequestContextListener.class,
-				RequestContextFilter.class })
-		public RequestContextFilter requestContextFilter() {
-			return new OrderedRequestContextFilter();
-		}
-
 		@Bean
 		@ConditionalOnBean(View.class)
 		@ConditionalOnMissingBean
@@ -312,6 +305,13 @@ public class WebMvcAutoConfiguration {
 			}
 		}
 
+		@Bean
+		@ConditionalOnMissingBean({ RequestContextListener.class,
+				RequestContextFilter.class })
+		public static RequestContextFilter requestContextFilter() {
+			return new OrderedRequestContextFilter();
+		}
+
 		@Configuration
 		@ConditionalOnProperty(value = "spring.mvc.favicon.enabled", matchIfMissing = true)
 		public static class FaviconConfiguration {