Adjust token json export for Figma

[mrkskmn]

The current token export as JSON file works when imported in Figma but is missing token aliases.
It would be desirable to tweak the exported JSON so that all the tokens reference the correct aliases when imported into Figma.

The export should be adjusted so it follows this format for aliases:

"theme": {
     "primary": {
       "bg": {
         "$type": "color",
         "$value": "{color.base.brand.400.value}",
         "cssProp": "primary-bg"
       }
}