Make inner classes static when feasible

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-webmvc/src/main/java/org/springframework/web/servlet/resource/VersionResourceResolver.java

@@ -232,7 +232,7 @@ public class VersionResourceResolver extends AbstractResourceResolver {
 	}
 
 
-	private class FileNameVersionedResource extends AbstractResource implements HttpResource {
+	private static class FileNameVersionedResource extends AbstractResource implements HttpResource {
 
 		private final Resource original;