Deprecate AppCacheManifestTransformer

This commit deprecates the `AppCacheManifestTransformer` implementations
since the appcache feature is being removed from the browsers.

Closes gh-25733

Author: bclozel

spring-webflux/src/main/java/org/springframework/web/reactive/resource/AppCacheManifestTransformer.java

@@ -65,7 +65,9 @@
  * @author Brian Clozel
  * @since 5.0
  * @see <a href="https://html.spec.whatwg.org/multipage/browsers.html#offline">HTML5 offline applications spec</a>
+ * @deprecated as of 5.3 since browser support is going away, scheduled for removal in 6.0.
  */
+@Deprecated
 public class AppCacheManifestTransformer extends ResourceTransformerSupport {
 
 	private static final String MANIFEST_HEADER = "CACHE MANIFEST";

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

@@ -62,7 +62,9 @@
  * @author Brian Clozel
  * @since 4.1
  * @see <a href="https://html.spec.whatwg.org/multipage/browsers.html#offline">HTML5 offline applications spec</a>
+ * @deprecated as of 5.3 since browser support is going away, scheduled for removal in 6.0.
  */
+@Deprecated
 public class AppCacheManifestTransformer extends ResourceTransformerSupport {
 
 	private static final String MANIFEST_HEADER = "CACHE MANIFEST";