Restructure web auto-configuration

Restructure `org.springframework.boot.autoconfigure.web` to better align
with the new package structure in `spring-boot`.

Auto-configuration is now split into client, servlet and reactive
sub-packages. In addition a new `http` package now handles common
HTTP concerns.

Fixes gh-8616

spring-boot-docs/src/test/java/org/springframework/boot/context/embedded/TomcatLegacyCookieProcessorExampleTests.java

@@ -16,8 +16,13 @@
 
 package org.springframework.boot.context.embedded;
 
+import java.net.URL;
+
 import org.apache.catalina.Context;
+import org.apache.catalina.webresources.TomcatURLStreamHandlerFactory;
 import org.apache.tomcat.util.http.LegacyCookieProcessor;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
 import org.junit.Test;
 
 import org.springframework.boot.SpringApplication;
@@ -28,6 +33,7 @@ import org.springframework.boot.web.server.WebServerFactoryCustomizerBeanPostPro
 import org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.test.util.ReflectionTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -38,6 +44,14 @@ import static org.assertj.core.api.Assertions.assertThat;
  */
 public class TomcatLegacyCookieProcessorExampleTests {
 
+	@BeforeClass
+	@AfterClass
+	public static void uninstallUrlStreamHandlerFactory() {
+		ReflectionTestUtils.setField(TomcatURLStreamHandlerFactory.class, "instance",
+				null);
+		ReflectionTestUtils.setField(URL.class, "factory", null);
+	}
+
 	@Test
 	public void cookieProcessorIsCustomized() {
 		ServletWebServerApplicationContext applicationContext = (ServletWebServerApplicationContext) new SpringApplication(