Export ...ParsedData interfaces (#12035)

Otherwise, trying to inherit from DatasetController in a TypeScript project may result in TypeScript errors similar to the following:

> error TS9006: Declaration emit for this file requires using private name 'RadialParsedData' from module '"/Users/joshkel/src/app/node_modules/chart.js/dist/types/index"'. An explicit type annotation may unblock declaration emit.