I had initially seen some oddities around type augmentation for type definitions in subdirectories of `types`, and using Rollup seemed to help with that. However, now that all of Chart.js's main types are directly under `types`, there seems to be no need for this.
This simplifies the build process, since it no longer needs to use rollup-plugin-dts.
It also improves some third-party tools. For example, I'm in the habit of using WebStorm's "Go To Declaration or Usages" hotkey with third-party TypeScript definitions as a quick way of getting more information about an API. With the Rollup-generate types, that works poorly; WebStorm goes to the imported-and-re-exported symbol within the barely-readable machine-generated dist/chart.esm.d.ts file, and I have to navigate two more hops to find the actual definitions.