feat: NucleusFonts

[Priva28]

This PR adds font styling definitions to Nucleus. It's designed to be flexible so it can work with multiple font families as well as with a range of configuration options.

The definitions for fonts live in tokens/definitions/font/fonts.json. This file should follow this format:

{
  "{{fontFamily}}": {
    "{{fontStyle}}": {
      "size": 13,
      "weight": 325,
      "letterSpacing": 0.0,
      "lineHeight": 1.3,
      "dynamicTypeStyle": "caption2"
    },
    {
      "b1": {
        ...
      }
    }
  }
}

Check https://developer.apple.com/design/human-interface-guidelines/typography#iOS-iPadOS-Dynamic-Type-sizes to set the right value for the dynamicTypeStyle.

---

The build script has been split into multiple files to handle generation for color and font. This will make it easier to expand upon moving forward.

On both iOS and Android we have the concept of a NucleusFont object. This is a simple object that provides the font styling values. It's the clients responsibility to actually render the font depending on these definitions.