refactor: align codebase on .ts vs .tsx on refactor branch

### Problem
The refactor branch uses `.tsx` for all file extensions. This is against existing standards which could make it difficult to tell where standalone TS code lives, and where JSX code lives.

There are also some small syntax changes: https://stackoverflow.com/questions/34224007/is-there-any-downside-to-using-tsx-instead-of-ts-all-the-times-in-typescript.

### Definition of Done
Refactor all `.tsx` files to use `.ts` that don't leverage JSX elements. This allows developers to know looking at the extension if a file is rendering components, or pure utility/functionality.