TS: String object type -> string literal type
TS: String object type -> string literal type

I suspect the use of the `String` object type was an accident of history. This PR makes moves to a more consistent use of types for literal types.

> Note: there is some [weirdness about type compatibility between `String` and `string`](https://www.typescriptlang.org/play/#code/C4TwDgpgBAhlC8UDKwBOBLAdgcyhAHsBJgCYDOUZaWuA-FAOQgRkNQBcjmA9gwNwAoUJCgAjBJWo48hYuWRS6jZqw5deg4dADGElBmkEipCvppR6TFm04Me-IA).

lloydbenson/lab,lloydbenson/lab,lloydbenson/lab