Fix generated build-info.json with correct icons and classification

[metonym]

This was flagged in #158 (review)

The current build-info.json generated by index.ts is used by the documentation site. The impact of this bug is that the documentation site for icons may omit/misclassify certain icons.

The current script relies on the module name from @carbon/icons/metadata.json to categorize modules into glyphs or icons. It should instead use the metadata from that file to determine the groupings.

{
  "name": "low-severity",
  "friendlyName": "Low severity",
  "sizes": [
    "glyph"
  ]
  // ...
}