Show progress indicator of "Run configurations..." after 800 ms

Wait a while before showing the progress indicator in the dialog "Run
configurations...". This avoids the flickering that happens when the
task is completed in under 800 ms (which is the current norm in
PlatformUI.getWorkbench().getProgressService().getLongOperationTime())

Contributes to eclipse-pde/eclipse.pde#679

debug/org.eclipse.debug.ui/ui/org/eclipse/debug/internal/ui/launchConfigurations/LaunchConfigurationsDialog.java

@@ -91,6 +91,7 @@
 import org.eclipse.swt.widgets.ToolBar;
 import org.eclipse.swt.widgets.TreeItem;
 import org.eclipse.ui.PlatformUI;
+import org.eclipse.ui.progress.UIJob;
 import org.eclipse.ui.progress.WorkbenchJob;
 import org.osgi.framework.FrameworkUtil;
 
@@ -1374,9 +1375,13 @@ public void run(boolean fork, boolean cancelable, IRunnableWithProgress runnable
 			if (cancelable) {
 				fProgressMonitorPart.attachToCancelComponent(null);
 			}
-			fProgressMonitorPart.getParent().setVisible(true);
+
 			fActiveRunningOperations++;
 
+			UIJob showProgressMonitorPart = createJobToShowProgressMonitorPart();
+			// only show the progress bar if necessary after 1 second
+			showProgressMonitorPart.schedule(PlatformUI.getWorkbench().getProgressService().getLongOperationTime());
+
 		//do work here collecting enabled states, otherwise to get these states we would need to
 		//perform the validation of the dialog again, which is expensive and would cause flashing of widgets.
 			Control[] children = ((Composite)fButtonComp.getChildren()[0]).getChildren();
@@ -1391,6 +1396,8 @@ public void run(boolean fork, boolean cancelable, IRunnableWithProgress runnable
 				ModalContext.run(runnable, fork, fProgressMonitorPart, getShell().getDisplay());
 			}
 			finally {
+				showProgressMonitorPart.cancel();
+
 				fActiveRunningOperations--;
 				updateRunnnableControls(true, prev);
 				if (getShell() != null) {
@@ -1409,6 +1416,17 @@ public void run(boolean fork, boolean cancelable, IRunnableWithProgress runnable
 		}
 	}
 
+	private UIJob createJobToShowProgressMonitorPart() {
+		return UIJob.create(IInternalDebugCoreConstants.EMPTY_STRING, __ -> {
+			// only show the progress monitor if there are still active operations by the
+			// time this job is executed
+			if (fActiveRunningOperations > 0) {
+				fProgressMonitorPart.getParent().setVisible(true);
+			}
+			return Status.OK_STATUS;
+		});
+	}
+
 	/**
 	 * Updates the enablement of the runnable controls to appear disabled as a job is running
 	 * @param enabled the desired enable status of the dialog area, revert//apply buttons, and