support font sizes provided by the class

[xworld21]

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LaTeXML pretends that the base font size is always 10pt, for simplicity, except for the a0poster class. This is quite inconvenient with TikZ and tikz-cd, because the figures are generated based on 10pt, even though they might have been written with 12pt in mind.

I am running some experiments with BookML and using the font sizes prescribed by the class options results in visible improvements.

Without adjusting for 12pt class option (top LaTeXML, bottom LaTeX+dvisvgm): After adjusting for 12pt:

(For both examples, the images have bene rescaled so that the characters have the same size as the surrounding HTML.)