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
return false;
		if (getClass() != obj.getClass())
			return false;
		final ViewerCell other = (ViewerCell) obj;
		if (columnIndex != other.columnIndex)
			return false;
		if (row == null) {
			if (other.row != null)
				return false;
		} else if (!row.equals(other.row))
			return false;
		return true;
	}
	private int getWidth() {
		return row.getWidth(columnIndex);
	}
	private boolean isVisible() {
		return getWidth() > 0;
	}
	/**
	 * Scroll the cell into view
	 * 
	 * @return true if the cell was scrolled into view
	 * @since 3.5
	 */
	public boolean scrollIntoView() {
		return row.scrollCellIntoView(columnIndex);
	}
}