Document Servlet PushBuilder API deprecation

See gh-33918

Author: bclozel

framework-docs/modules/ROOT/pages/web/webmvc/mvc-controller/ann-methods/arguments.adoc

@@ -30,8 +30,7 @@ and others) and is equivalent to `required=false`.
 
 | `jakarta.servlet.http.PushBuilder`
 | Servlet 4.0 push builder API for programmatic HTTP/2 resource pushes.
-  Note that, per the Servlet specification, the injected `PushBuilder` instance can be null if the client
-  does not support that HTTP/2 feature.
+  Note that this API has been deprecated as of Servlet 6.1.
 
 | `java.security.Principal`
 | Currently authenticated user -- possibly a specific `Principal` implementation class if known.

framework-docs/modules/ROOT/pages/web/webmvc/mvc-http2.adoc

@@ -4,12 +4,8 @@
 
 [.small]#xref:web/webflux/http2.adoc[See equivalent in the Reactive stack]#
 
-Servlet 4 containers are required to support HTTP/2, and Spring Framework 5 is compatible
-with Servlet API 4. From a programming model perspective, there is nothing specific that
+Servlet 4 containers are required to support HTTP/2, and Spring Framework requires
+Servlet API 6.1. From a programming model perspective, there is nothing specific that
 applications need to do. However, there are considerations related to server configuration.
 For more details, see the
 {spring-framework-wiki}/HTTP-2-support[HTTP/2 wiki page].
-
-The Servlet API does expose one construct related to HTTP/2. You can use the
-`jakarta.servlet.http.PushBuilder` to proactively push resources to clients, and it
-is supported as a xref:web/webmvc/mvc-controller/ann-methods/arguments.adoc[method argument] to `@RequestMapping` methods.

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ServletRequestMethodArgumentResolverTests.java

@@ -69,6 +69,7 @@ class ServletRequestMethodArgumentResolverTests {
 
 
 	@BeforeEach
+	@SuppressWarnings("deprecation")
 	void setup() throws Exception {
 		resolver = new ServletRequestMethodArgumentResolver();
 		mavContainer = new ModelAndViewContainer();
@@ -241,6 +242,7 @@ void httpMethod() throws Exception {
 	}
 
 	@Test
+	@SuppressWarnings("deprecation")
 	void pushBuilder() throws Exception {
 		final PushBuilder pushBuilder = mock();
 		servletRequest = new MockHttpServletRequest("GET", "") {
@@ -259,7 +261,7 @@ public PushBuilder newPushBuilder() {
 	}
 
 
-	@SuppressWarnings("unused")
+	@SuppressWarnings({"unused", "deprecation"})
 	public void supportedParams(ServletRequest p0,
 								MultipartRequest p1,
 								HttpSession p2,