[FEATURE] Add font fallback

[kaiquegazola]

Describe your feature request

When rendering data, we may encounter glyphs/chars that are not available in main style font, an example:

Html(
      data: '<span>‟Pessoas que se recuperaram, »’”›⸃⸅⸊⸍⸝⸡ [...]”</span>',
      style: <String, Style>{
        'span': Style(
          fontFamily: 'Lato',
        ),
      },
);

and will render this:

Proposal
Flutter TextStyle already solves this with the fontFamilyFallback parameter, just need to expose it to flutter_html Style.

A picture of a cute animal (not mandatory but encouraged)