Stop using TypeDoc "library mode"

[carnesen]

This project uses TypeDoc to generate API documentation from TSDoc comments in the code. Unfortunately specifically it uses in "library mode", which was released in a TypeDoc 0.20 beta but didn't make it into the actual release since --mode was removed. For more information see TypeStrong/typedoc#1184 and https://github.com/TypeStrong/typedoc/releases/tag/v0.20.0 . This task will be complete when we are no longer using TypeDoc's "library mode".