Add missing elements in util/mxXYZCanvas2D

[tbouffard]

I have detected this while trying to integrate mxgraph-type-defintiions in https://github.com/process-analytics/bpmn-visualization-js/pull/301

• missing methods in mxAbstractCanvas2D: because of abstractness is missing in mxGraph JavaScript code (ES5), some methods like fill or stroke are missing (the mxGraph JS API states to have a look at mxXmlCanvas2D to know the public API of it :disappointed: )
• missing mxXmlCanvas2D type
• review needed on types used by mxSvgCanvas2D and mxVmlCanvas2D

[tbouffard]

@hungtcs just prompt to not conflict, I am preparing a PR about this