Bug 267117 [JFace] Provide possibility for subclasses to check if a column is visible in ViewerRow
Currently this is decided by checking with width but this makes Nebula-Grid fail.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerCell.java
public Object getElement() {
		if (element != null) {
			return element;
		}
		if (row != null) {
			return row.getElement();
		}
		return null;
	}
	/**
	 * Return the text for the cell.
	 * 
	 * @return {@link String}
	 */
	public String getText() {
		return row.getText(columnIndex);
	}
	/**
	 * Return the Image for the cell.
	 * 
	 * @return {@link Image} or <code>null</code>
	 */
	public Image getImage() {
		return row.getImage(columnIndex);
	}
	/**
	 * Set the background color of the cell.
	 * 
	 * @param background
	 */