Support ambiguous syntax for Font properties

[Dekkonot]

Given how unambiguous Font as a datatype actually is, it makes not very much sense to require people use the fully qualified syntax for FontFace and any other properties that come up. So, this PR adds a new ambiguous syntax that supports it.

Long-term, I think we should reconsider our strategy for font families to make it more obvious how to set them (maybe use an enum instead of a raw string?) but that's an issue for another day.

[kennethloeffler]

Long-term, I think we should reconsider our strategy for font families to make it more obvious how to set them (maybe use an enum instead of a raw string?) but that's an issue for another day.

The Font type in Roblox's Lua API also uses content URIs for font families, so I don't think it will be too surprising, as long as it's documented!

[Dekkonot]

I don't think it's surprising necessarily, it's just rather inconvenient to have to specify a path to a JSON! Roblox offers Font.fromEnum and Font.fromName as convenience functions and I think it'd be nice to have something similar for Rojo users. That's out of scope for this PR though.

[Dekkonot]

bruh.

[kennethloeffler]

Tested building an rbxm from

{
  "name": "TextBox",
  "tree": {
    "$className": "TextBox",
    "$properties": {
      "FontFace": {
        "family": "rbxasset://fonts/families/RobotoMono.json",
        "weight": "Thin",
        "style": "Normal"
      }
    }
  }
}

and was successful, lgtm