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
* 
	 * @param row
	 * @param columnIndex
	 */
	ViewerCell(ViewerRow row, int columnIndex, Object element) {
		this.row = row;
		this.columnIndex = columnIndex;
		this.element = element;
	}
	/**
	 * Get the index of the cell.
	 * 
	 * @return the index
	 */
	public int getColumnIndex() {
		return columnIndex;
	}
	/**
	 * Get the bounds of the cell.
	 * 
	 * @return {@link Rectangle}
	 */
	public Rectangle getBounds() {
		return row.getBounds(columnIndex);
	}
	/**
	 * Get the element this row represents.
	 * 
	 * @return {@link Object}
	 */