Switch to use a .d.ts file to define the parse trees

Instead of using a json file we now use a simple .d.ts file of
the form:

  interface ArrayLiteralExpression {
    location: SourceRange;
    elements: Array<ParseTree>;
  }

compared to the old json form:

  "ArrayLiteralExpression": {
    "location": [
      "SourceRange"
    ],
    "elements": [
      "Array<ParseTree>"
    ]
  },

At this point we still generate the json file but we could update
the other build scripts to read directly from the .d.ts. file
instead.