Add character widths for "Red Hat Text" font

[dlabrecq]

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Feature Request

We're using the "Red Hat Text" font in our custom theme. However, the `TextSize.approximateTextSize` function defaults to using font widths for Helvetica.

To achieve proper text sizing, I'd like to add character widths for the "Red Hat Text" font to packages/victory-core/src/victory-util/textsize.js.

Google fonts
https://fonts.google.com/specimen/Red+Hat+Text?preview.text=Redhattext