Update API version and package references for Jakarta EE 9

Closes gh-27689
See gh-25354

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

@@ -364,7 +364,7 @@ public class DispatcherServlet extends FrameworkServlet {
 
 	/**
 	 * Create a new {@code DispatcherServlet} with the given web application context. This
-	 * constructor is useful in Servlet 3.0+ environments where instance-based registration
+	 * constructor is useful in Servlet environments where instance-based registration
 	 * of servlets is possible through the {@link ServletContext#addServlet} API.
 	 * <p>Using this constructor indicates that the following properties / init-params
 	 * will be ignored:

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

@@ -249,7 +249,7 @@ public abstract class FrameworkServlet extends HttpServletBean implements Applic
 
 	/**
 	 * Create a new {@code FrameworkServlet} with the given web application context. This
-	 * constructor is useful in Servlet 3.0+ environments where instance-based registration
+	 * constructor is useful in Servlet environments where instance-based registration
 	 * of servlets is possible through the {@link ServletContext#addServlet} API.
 	 * <p>Using this constructor indicates that the following properties / init-params
 	 * will be ignored:

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestPartMethodArgumentResolver.java

@@ -46,7 +46,7 @@ import org.springframework.web.multipart.support.RequestPartServletServerHttpReq
  * <ul>
  * <li>Annotated with @{@link RequestPart}
  * <li>Of type {@link MultipartFile} in conjunction with Spring's {@link MultipartResolver} abstraction
- * <li>Of type {@code jakarta.servlet.http.Part} in conjunction with Servlet 3.0 multipart requests
+ * <li>Of type {@code jakarta.servlet.http.Part} in conjunction with Servlet multipart requests
  * </ul>
  *
  * <p>When a parameter is annotated with {@code @RequestPart}, the content of the part is

spring-webmvc/src/main/java/org/springframework/web/servlet/support/RequestContextUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -105,8 +105,6 @@ public abstract class RequestContextUtils {
 	 * that has initiated request processing, and for the global context if none
 	 * was found associated with the current request. The global context will
 	 * be found via the ServletContext or via ContextLoader's current context.
-	 * <p>NOTE: This variant requires Servlet 3.0+ and is generally recommended
-	 * for forward-looking custom user code.
 	 * @param request current HTTP request
 	 * @return the request-specific WebApplicationContext, or the global one
 	 * if no request-specific context has been found, or {@code null} if none