fix: make mxText assignable to mxShape

[tbouffard]

Some fields were redeclared as protected whereas there are public in the mxShape
super class.

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Introduced in 1.0.1 by #32
Detected with process-analytics/bpmn-visualization-js#1224

cc @csouchet @aibcmars

[hungtcs]

Hi @tbouffard, these parameters are inferred from mxText.js#L65-L86, it seems that all properties should be public, I added a patch to to modify all of them.

[tbouffard]

@hungtcs thanks for merging and the patch.
About protected visibility, I introduced it in #32 and I don't remember why I didn't set it to public. But anyway, you fix it for good: there was no reason to put them protected and we don't have protected elsewhere in the rest of the types.