Filip ts config cleanup all

[sodic]

This PR contains all the changes from:

• TS Config cleanup - Part 1 #2393
• TS config cleanup - Part 2 #2407
• TS Config cleanup - Part 3 #2410

I merged it all into a single PR before merging into main to avoid dealing with false-positive conflicts caused by squashes.

I verified that the refactor didn't change the code's behavior by:

• Writing a complex app using Wasp's TS config (i.e., translated waspc/todoApp)
• Generating the decls.json file with Wasp 0.15.2
• Generating the decls.json file with the repo version of Wasp
• Comparing those files

Here's the result

$ shasum decls*
4ea44d8f1ec7e8c644dc862c09531ce515ce8550  decls-new.json
4ea44d8f1ec7e8c644dc862c09531ce515ce8550  decls-old.json