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/ViewerRow.java
/**
	 * Get the foreground at the columnIndex.
	 * 
	 * @param columnIndex
	 * @return {@link Color} or <code>null</code>
	 */
	public abstract Color getForeground(int columnIndex);
	/**
	 * Set the foreground at the columnIndex.
	 * 
	 * @param columnIndex
	 * @param color
	 */
	public abstract void setForeground(int columnIndex, Color color);
	/**
	 * Get the font at the columnIndex.
	 * 
	 * @param columnIndex
	 * @return {@link Font} or <code>null</code>
	 */
	public abstract Font getFont(int columnIndex);
	/**
	 * Set the {@link Font} at the columnIndex.
	 * 
	 * @param columnIndex
	 * @param font
	 */
	public abstract void setFont(int columnIndex, Font font);
	/**
	 * Get the ViewerCell at point.