Add support for fonts in math text

For all non math text rendered by matplotlib, use vtkMatplotlibMathTextUtilities::GetFontProperties to construct the pyFont object and use matplotlib.mathtext parse method instead of to_mask to use the pyFont object.

For math text (inside a ...), use predefined fonts (stix, dejavusans, computer modern). You can set the text to bold using \mathbf{boldText}, to italic using \mathit{italicText}, etc... See https://matplotlib.org/stable/tutorials/text/mathtext.html.

Also raise a warning when the text property uses Shadows as it is unsupported with math text.