Just want to leave the note here that I finally found a satisfactory solution for how to
- write all user scripts in Typescript
- organize the code into multiple scripts
- compile and bundle all source files into a single Javascript file that can be imported into Drafts actions
For that, I use the Rollup bundler. You can find the configuration in my GitHub Repository, the Readme provides some additional instructions.
Thanks to all of you for your helpful advice along the way!