Make "Compare with Clipboard" work in active editor of FormEditor

e.g. m2e's MavenPomEditor or PDE's ManifestEditor

Signed-off-by: Till Brychcy <[email protected]>

Author: brychcy

team/bundles/org.eclipse.compare/compare/org/eclipse/compare/internal/ClipboardCompare.java

@@ -43,6 +43,7 @@
 import org.eclipse.ui.IWorkbenchPage;
 import org.eclipse.ui.IWorkbenchPart;
 import org.eclipse.ui.PlatformUI;
+import org.eclipse.ui.forms.editor.FormEditor;
 import org.eclipse.ui.texteditor.ITextEditor;
 
 public class ClipboardCompare extends BaseCompareAction implements IObjectActionDelegate {
@@ -88,6 +89,9 @@ private void processComparison(IFile file, Shell parentShell) throws IOException
 			return;
 		}
 		final String selectionContents;
+		if (editor instanceof FormEditor fromEditor) {
+			editor = fromEditor.getActiveEditor();
+		}
 		if (editor instanceof ITextEditor txtEditor) {
 			ISelection selection = txtEditor.getSelectionProvider().getSelection();
 			if (selection instanceof ITextSelection textSelection) {