[FEAT] Add padding/margin to the default Badge Overlay

[tbouffard]

Is your feature request related to a problem? Please describe. The current default badge displays the overlay text to close from the border. This is particularly visible with the default white fill and black stroke colors. This would be less visible with alternate colors, especially if the fill and stroke colors were the same (#1172)

Describe the solution you'd like Set default padding/margin to add more spaces between the text and the border. Desicion of making the value configurable is deferred to #1172

This would look like the following when applied to the 2 previous examples

[NathalieC]

that's exactly what I meant. Thanks.

[aibcmars]

it seems that in mxSvgCanvas2D.prototype.addTextBackground method (which is used for adding the background for the node for mxText shape) there is no use of spacing - some magic number '2' appears (it can be modified to add missing right padding)

	n.setAttribute('width', Math.ceil(bbox.width + 2));
	n.setAttribute('height', Math.ceil(bbox.height));