[FEAT] render shape label height bounds

[tbouffard]

As of #299, the height of the label is the height of its related shape.
This is the way mxGraph 4.1.0 is working: there is no possibility to pass a label height and the shape height is used

Notice that label height is only required if we want to support clipping/truncating/ellipsing based on BPMN label height value. Currently, this would use the shape height.

mxgraph 4.1.1 label position computation

See

• mxCellRenderer.prototype.getLabelBounds
• mxGraphView.prototype.updateVertexLabelOffset : use label width and label position
• mxGraphView.prototype.updateEdgeLabelOffset