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
if ((directionMask & ABOVE) == ABOVE) {
			row = this.row.getNeighbor(ViewerRow.ABOVE, sameLevel);
		} else if ((directionMask & BELOW) == BELOW) {
			row = this.row.getNeighbor(ViewerRow.BELOW, sameLevel);
		} else {
			row = this.row;
		}
		if (row != null) {
			int columnIndex;
			columnIndex = getVisualIndex();
			int modifier = 0;
			if ((directionMask & LEFT) == LEFT) {
				modifier = -1;
			} else if ((directionMask & RIGHT) == RIGHT) {
				modifier = 1;
			}
			columnIndex += modifier;
			if (columnIndex >= 0 && columnIndex < row.getColumnCount()) {
				ViewerCell cell = row.getCellAtVisualIndex(columnIndex);
				if (cell != null) {
					while (cell != null
							&& columnIndex < row.getColumnCount() - 1
							&& columnIndex > 0) {
						if (cell.isVisible()) {
							break;
						}
						columnIndex += modifier;
						cell = row.getCellAtVisualIndex(columnIndex);
						if (cell == null) {
							break;