[GEF] Fully migrate to the GEF TreeViewer

This removes our copy of the `TreeViewerEditPart` and `TreeViewer` in
favor of the upstream classes. In order to use the GEF viewer directly,
a virtual `DesignComponent` edit part needs to be used as contents,
holding the `Tree` widget. Otherwise the edit part of the first model is
not shown.

Author: ptziegler

org.eclipse.wb.core.java/src/org/eclipse/wb/internal/core/gef/tools/TabOrderTool.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2011, 2025 Google, Inc. and others.
+ * Copyright (c) 2011, 2026 Google, Inc. and others.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
@@ -195,8 +195,7 @@ protected boolean handleButtonDown(int button) {
 	@Override
 	protected void updateTargetUnderMouse() {
 		// find on clickable layer
-		EditPart editPart =
-				getCurrentViewer().findObjectAtExcluding(
+		EditPart editPart = ((IEditPartViewer) getCurrentViewer()).findObjectAtExcluding(
 						getLocation(),
 						getExclusionSet(),
 						getTargetingConditional(),

org.eclipse.wb.core.java/src/org/eclipse/wb/internal/core/gefTree/EditPartFactory2.java

@@ -19,9 +19,9 @@
 import org.eclipse.wb.internal.core.gefTree.part.FlowContainerGroupEditPart;
 import org.eclipse.wb.internal.core.model.nonvisual.AbstractArrayObjectInfo;
 import org.eclipse.wb.internal.core.model.nonvisual.FlowContainerGroupInfo;
-import org.eclipse.wb.internal.gef.tree.TreeViewer;
 
 import org.eclipse.gef.EditPart;
+import org.eclipse.gef.ui.parts.TreeViewer;
 
 /**
  * Generic implementation of {@link IEditPartFactory} for {@link TreeViewer} that redirects

org.eclipse.wb.core/META-INF/MANIFEST.MF

@@ -495,7 +495,6 @@ Export-Package: org.eclipse.wb.core.branding,
    org.eclipse.wb.swing,
    org.eclipse.wb.swt",
  org.eclipse.wb.internal.gef.graphical;x-friends:="org.eclipse.wb.tests,org.eclipse.wb.core.java",
- org.eclipse.wb.internal.gef.tree;x-friends:="org.eclipse.wb.tests,org.eclipse.wb.core.java",
  org.eclipse.wb.internal.gef.tree.dnd;x-friends:="org.eclipse.wb.core.databinding,org.eclipse.wb.core.java,org.eclipse.wb.tests",
  org.eclipse.wb.internal.gef.tree.policies;x-internal:=true,
  org.eclipse.wb.internal.gef.tree.tools;x-internal:=true

org.eclipse.wb.core/src-gef/org/eclipse/wb/gef/core/tools/Tool.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2011, 2025 Google, Inc. and others.
+ * Copyright (c) 2011, 2026 Google, Inc. and others.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License 2.0 which is available at
@@ -69,13 +69,6 @@ public final boolean isActive() {
 		return getFlag(FLAG_ACTIVE);
 	}
 
-	/**
-	 * Get {@link IEditPartViewer}.
-	 */
-	public final IEditPartViewer getCurrentViewer() {
-		return (IEditPartViewer) super.getCurrentViewer();
-	}
-
 	/**
 	 * Returns the {@link EditDomain}.
 	 */

org.eclipse.wb.core/src-gef/org/eclipse/wb/gef/tree/DesignTreeEditPart.java

@@ -19,6 +19,8 @@
 import org.eclipse.gef.EditPolicy;
 import org.eclipse.gef.Request;
 import org.eclipse.gef.commands.Command;
+import org.eclipse.gef.editparts.AbstractTreeEditPart;
+import org.eclipse.swt.widgets.TreeItem;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -28,8 +30,12 @@
  *
  * @see {@link RequestProcessor}
  */
-@SuppressWarnings("removal")
-public abstract class DesignTreeEditPart extends TreeEditPart {
+public abstract class DesignTreeEditPart extends AbstractTreeEditPart {
+
+	@Override
+	public TreeItem getWidget() {
+		return (TreeItem) super.getWidget();
+	}
 
 	////////////////////////////////////////////////////////////////////////////
 	//

org.eclipse.wb.core/src-gef/org/eclipse/wb/gef/tree/TreeEditPart.java

@@ -18,7 +18,6 @@
 import org.eclipse.wb.gef.core.requests.CreateRequest;
 import org.eclipse.wb.gef.core.requests.PasteRequest;
 import org.eclipse.wb.internal.core.EnvironmentUtils;
-import org.eclipse.wb.internal.gef.tree.TreeViewer;
 
 import org.eclipse.draw2d.geometry.Point;
 import org.eclipse.draw2d.geometry.Rectangle;
@@ -30,6 +29,7 @@
 import org.eclipse.gef.commands.Command;
 import org.eclipse.gef.editpolicies.AbstractEditPolicy;
 import org.eclipse.gef.requests.DropRequest;
+import org.eclipse.gef.ui.parts.TreeViewer;
 import org.eclipse.swt.dnd.DND;
 import org.eclipse.swt.widgets.Tree;
 import org.eclipse.swt.widgets.TreeItem;