feat: check if GoogleFonts supports a font before generating

[timcreatedit]

figmage/lib/src/data/generators/text_style_theme_extension_generator.dart

Line 44 in f69145c

// TODO(tim): bring this back once dependcies are resolved

The code for this is already there, but we can't depend on google_fonts at the moment because figmage is a pure dart package and Google Fonts depends on the Flutter SDK.

So we should evaluate if it makes sense to turn figmage into a Flutter package, or check google fonts in another way (REST request or sth)