SPARK-3996: Add jetty servlet and continuations.

These are needed transitively from the other Jetty libraries
we include. It was not picked up by unit tests because we
disable the UI.

Author: Patrick Wendell <patrick@databricks.com>

Closes #4323 from pwendell/jetty and squashes the following commits:

d8669da [Patrick Wendell] SPARK-3996: Add jetty servlet and continuations.

core/pom.xml

@@ -122,6 +122,16 @@
       <artifactId>jetty-http</artifactId>
       <scope>compile</scope>
     </dependency>
+    <dependency>
+      <groupId>org.eclipse.jetty</groupId>
+      <artifactId>jetty-continuation</artifactId>
+      <scope>compile</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.eclipse.jetty</groupId>
+      <artifactId>jetty-servlet</artifactId>
+      <scope>compile</scope>
+    </dependency>
 
     <dependency>
       <groupId>org.apache.commons</groupId>
@@ -377,7 +387,7 @@
               <overWriteIfNewer>true</overWriteIfNewer>
               <useSubDirectoryPerType>true</useSubDirectoryPerType>
               <includeArtifactIds>
-                guava,jetty-io,jetty-http,jetty-plus,jetty-util,jetty-server
+                guava,jetty-io,jetty-servlet,jetty-continuation,jetty-http,jetty-plus,jetty-util,jetty-server
               </includeArtifactIds>
               <silent>true</silent>
             </configuration>

pom.xml

@@ -347,6 +347,18 @@
         <version>${jetty.version}</version>
         <scope>provided</scope>
       </dependency>
+      <dependency>
+        <groupId>org.eclipse.jetty</groupId>
+        <artifactId>jetty-continuation</artifactId>
+        <version>${jetty.version}</version>
+        <scope>provided</scope>
+      </dependency>
+      <dependency>
+        <groupId>org.eclipse.jetty</groupId>
+        <artifactId>jetty-servlet</artifactId>
+        <version>${jetty.version}</version>
+        <scope>provided</scope>
+      </dependency>
       <dependency>
         <groupId>org.eclipse.jetty</groupId>
         <artifactId>jetty-util</artifactId>
@@ -1297,6 +1309,8 @@
 
               <include>org.eclipse.jetty:jetty-io</include>
               <include>org.eclipse.jetty:jetty-http</include>
+              <include>org.eclipse.jetty:jetty-continuation</include>
+              <include>org.eclipse.jetty:jetty-servlet</include>
               <include>org.eclipse.jetty:jetty-plus</include>
               <include>org.eclipse.jetty:jetty-security</include>
               <include>org.eclipse.jetty:jetty-util</include>

streaming/pom.xml

@@ -62,6 +62,10 @@
       <groupId>org.eclipse.jetty</groupId>
       <artifactId>jetty-http</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.eclipse.jetty</groupId>
+      <artifactId>jetty-servlet</artifactId>
+    </dependency>
     <!-- End of shaded deps. -->
 
     <dependency>

yarn/pom.xml

@@ -80,6 +80,10 @@
       <groupId>org.eclipse.jetty</groupId>
       <artifactId>jetty-http</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.eclipse.jetty</groupId>
+      <artifactId>jetty-servlet</artifactId>
+    </dependency>
     <!-- End of shaded deps. -->
 
     <dependency>