Fix traverse in multi page editors

control.traverse on a CTabFolder in the MultiPageEditor is navigation up the the outer CTabFolder itself.

This is causing several issues:
Setting the page for example to the second-to-last is changing the page in the multipage editor. Then the traverse direction is changed causing the outer tab to move in the wrong direction.
Furthermore on the outer tab you cannot jump from the last tab to the very first tab.

Author: Christopher-Hermann

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/handlers/TraversePageHandler.java

@@ -41,6 +41,15 @@ public final Object execute(final ExecutionEvent event) {
 			int traversalDirection = translateToTraversalDirection(forward);
 			Control control = focusControl;
 			do {
+				if (control instanceof CTabFolder folder && !isRootCTabFolder(folder)) {
+					// For multi-page editors, we want to skip inner CTabFolders
+					// If not skipped there are two issues:
+					// 1. loopToFirstOrLastItem would change the selection of the inner CTabFolder
+					// 2. control.traverse itself would navigate up to the outer CTabFolder and
+					// navigate there
+					control = control.getParent();
+					continue;
+				}
 				if (control instanceof CTabFolder folder && isFinalItemInCTabFolder(folder, forward)
 						&& !hasHiddenItem(folder)) {
 					loopToFirstOrLastItem(folder, forward);
@@ -59,6 +68,15 @@ public final Object execute(final ExecutionEvent event) {
 		return null;
 	}
 
+	private boolean isRootCTabFolder(CTabFolder folder) {
+		for (var current = folder.getParent(); current != null; current = current.getParent()) {
+			if (current instanceof CTabFolder) {
+				return false;
+			}
+		}
+		return true;
+	}
+
 	private boolean hasHiddenItem(CTabFolder folder) {
 		return Arrays.stream(folder.getItems()).anyMatch(i -> !i.isShowing());
 	}