[GTK] Tree and table only react delayed on mouse selection if drag listener is configured

[tmssngr]

Describe the bug
Normally, a Tree or Table immediately selects a row on mouse-down. However, this is not the case any more if a drag listener is added to the tree or table.

To Reproduce

• run this snippet

import org.eclipse.swt.*;
import org.eclipse.swt.dnd.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

public class TreeTableDnD {

	public static void main(String[] args) {
		final Display display = new Display();

		final Shell shell = new Shell(display);
		shell.setLayout(new FillLayout());

		final Tree tree = new Tree(shell, SWT.BORDER | SWT.V_SCROLL | SWT.H_SCROLL);
		for (int i = 0; i < 4; i++) {
			final TreeItem item = new TreeItem(tree, 0);
			item.setText("TreeItem " + i);
		}
		tree.addListener(SWT.Selection, e -> System.out.println("Tree selection changed"));

		final Table table = new Table(shell, SWT.BORDER | SWT.V_SCROLL | SWT.H_SCROLL);
		final TableColumn column = new TableColumn(table, SWT.DEFAULT);
		column.setText("Column");
		column.setWidth(250);
		table.setHeaderVisible(true);
		for (int i = 0; i < 4; i++) {
			final TableItem item = new TableItem(table, 0);
			item.setText("Item " + i);
		}
		table.addListener(SWT.Selection, e -> System.out.println("Table selection changed"));

//		new DragSource(tree, DND.DROP_MOVE).setTransfer(TextTransfer.getInstance());
//		new DragSource(table, DND.DROP_MOVE).setTransfer(TextTransfer.getInstance());

		shell.setSize(500, 300);
		shell.open();

		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) {
				display.sleep();
			}
		}

		display.dispose();
	}
}

• select a tree or table row with a slow mouse click -> the visible selection occurs immediately on mouse-down, the selection event is sent delayed
• now remove the comments to active the drag listener and try again -> the visually selection occurs delayed and the selection event even more delayed

Expected behavior
The tree and table rows get visually selected immediately and the selection event is sent immediately, independent of a drag listener.

Environment:

1. Select the platform(s) on which the behavior is seen:

• • All OS
• • Windows
• • Linux
• • macOS

2. Additional OS info (e.g. OS version, Linux Desktop, etc)
   Tried on Linux Mint (X11)