Use correct TreeElement and server-side classname (#9221)

* Use correct TreeElement and server-side classname
* Re-enable test, remove unnecessary imports

testbench-api/src/main/java/com/vaadin/testbench/elements/TreeElement.java

@@ -35,8 +35,7 @@ import com.vaadin.testbench.elementsbase.ServerClass;
  * @author Vaadin Ltd.
  * @since 8.1
  */
-// TODO: Switch to com.vaadin.ui.Tree once inheritance finding is fixed
-@ServerClass("com.vaadin.ui.Composite")
+@ServerClass("com.vaadin.ui.Tree")
 public class TreeElement extends AbstractComponentElement {
 
     /**

uitest/src/test/java/com/vaadin/tests/components/tree/TreeBasicFeaturesTest.java

@@ -5,7 +5,6 @@ import java.util.function.Predicate;
 
 import org.junit.Assert;
 import org.junit.Before;
-import org.junit.Ignore;
 import org.junit.Test;
 import org.openqa.selenium.By;
 
@@ -55,8 +54,6 @@ public class TreeBasicFeaturesTest extends MultiBrowserTest {
     }
 
     @Test
-    // TODO: Re-enable once cache issue is fixed.
-    @Ignore("Recent change to cache invalidation broke resource clean up.")
     public void tree_expand_all_with_icons() throws IOException {
         selectMenuPath("Component", "Icons", "By Depth");
         Assert.assertTrue("Icon not present", $(TreeElement.class).first()

uitest/src/test/java/com/vaadin/tests/contextclick/TreeContextClickTest.java

@@ -24,7 +24,7 @@ import org.openqa.selenium.WebElement;
 import org.openqa.selenium.interactions.Actions;
 
 import com.vaadin.testbench.By;
-import com.vaadin.testbench.elements.TreeElement;
+import com.vaadin.v7.testbench.elements.TreeElement;
 
 public class TreeContextClickTest extends AbstractContextClickTest {
 

uitest/src/test/java/com/vaadin/tests/themes/valo/ValoThemeUITest.java

@@ -26,9 +26,9 @@ import com.vaadin.testbench.elements.ButtonElement;
 import com.vaadin.testbench.elements.CheckBoxElement;
 import com.vaadin.testbench.elements.CssLayoutElement;
 import com.vaadin.testbench.elements.LabelElement;
-import com.vaadin.testbench.elements.TreeElement;
 import com.vaadin.testbench.parallel.Browser;
 import com.vaadin.tests.tb3.MultiBrowserTest;
+import com.vaadin.v7.testbench.elements.TreeElement;
 
 public class ValoThemeUITest extends MultiBrowserTest {
 

uitest/src/test/java/com/vaadin/v7/tests/components/tree/TreeItemSelectionWithoutImmediateTest.java

@@ -24,7 +24,6 @@ import org.openqa.selenium.interactions.Actions;
 
 import com.vaadin.testbench.By;
 import com.vaadin.tests.tb3.MultiBrowserTest;
-import com.vaadin.v7.tests.components.tree.TreeItemSelectionWithoutImmediate;
 
 public class TreeItemSelectionWithoutImmediateTest extends MultiBrowserTest {
 

uitest/src/test/java/com/vaadin/v7/tests/components/tree/TreeScrollingOnRightClickTest.java

@@ -25,7 +25,6 @@ import org.openqa.selenium.WebElement;
 import org.openqa.selenium.interactions.Actions;
 
 import com.vaadin.tests.tb3.MultiBrowserTest;
-import com.vaadin.v7.tests.components.tree.TreeScrollingOnRightClick;
 
 /**
  *