Migrate ApplicationContext to common hierarchy

This commit migrates `AnnotationConfigReactiveWebApplicationContext`
parent to the `GenericApplicationContext` abstraction. Any use of
`AnnotationConfigWebApplicationContext` is also removed as it also
inherits from the `AbstractRefreshableApplicationContext` outdated
hierarchy.

A new `AnnotationConfigServletWebApplicationContext` context is
introduced instead, extending from `GenericApplicationContext` and
providing the counter part of the reactive context for the Servlet-based
web app tests.

See gh-16096

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/servlet/SpringBootMockMvcBuilderCustomizerTests.java

@@ -27,13 +27,13 @@ import javax.servlet.http.HttpServlet;
 import org.junit.Test;
 
 import org.springframework.boot.web.servlet.FilterRegistrationBean;
+import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.mock.web.MockServletContext;
 import org.springframework.test.util.ReflectionTestUtils;
 import org.springframework.test.web.servlet.setup.DefaultMockMvcBuilder;
 import org.springframework.test.web.servlet.setup.MockMvcBuilders;
-import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -49,7 +49,7 @@ public class SpringBootMockMvcBuilderCustomizerTests {
 	@Test
 	@SuppressWarnings("unchecked")
 	public void customizeShouldAddFilters() {
-		AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
+		AnnotationConfigServletWebApplicationContext context = new AnnotationConfigServletWebApplicationContext();
 		MockServletContext servletContext = new MockServletContext();
 		context.setServletContext(servletContext);
 		context.register(ServletConfiguration.class, FilterConfiguration.class);