Move tomcat websocket dependency

Relocate tomcat-embed-websocket from spring-boot-starter-websocket
to spring-boot-starter-tomcat.

Fixes gh-1847

spring-boot-integration-tests/src/test/java/org/springframework/boot/gradle/WarPackagingTests.java

@@ -48,7 +48,8 @@ public class WarPackagingTests {
 
 	private static final Set<String> TOMCAT_EXPECTED_IN_WEB_INF_LIB_PROVIDED = new HashSet<String>(
 			Arrays.asList("spring-boot-starter-tomcat-", "tomcat-embed-core-",
-					"tomcat-embed-el-", "tomcat-embed-logging-juli-"));
+					"tomcat-embed-el-", "tomcat-embed-logging-juli-",
+					"tomcat-embed-websocket-"));
 
 	private static final Set<String> JETTY_EXPECTED_IN_WEB_INF_LIB_PROVIDED = new HashSet<String>(
 			Arrays.asList("spring-boot-starter-jetty-", "jetty-util-", "jetty-xml-",

spring-boot-starters/spring-boot-starter-tomcat/pom.xml

@@ -30,5 +30,9 @@
 			<groupId>org.apache.tomcat.embed</groupId>
 			<artifactId>tomcat-embed-logging-juli</artifactId>
 		</dependency>
+		<dependency>
+			<groupId>org.apache.tomcat.embed</groupId>
+			<artifactId>tomcat-embed-websocket</artifactId>
+		</dependency>
 	</dependencies>
 </project>

spring-boot-starters/spring-boot-starter-websocket/pom.xml

@@ -40,9 +40,5 @@
 			<groupId>org.springframework</groupId>
 			<artifactId>spring-websocket</artifactId>
 		</dependency>
-		<dependency>
-			<groupId>org.apache.tomcat.embed</groupId>
-			<artifactId>tomcat-embed-websocket</artifactId>
-		</dependency>
 	</dependencies>
 </project>