Fix type import errors due to usage of "exports" in package.json

[mattvague]

Summary

Add "types" field to "exports" to fix type imports

Description

I was having trouble getting the mathjs typescript types working in my app:

I previously worked around this by adding this to my tsconfig.json

But that was a bit hacky and started causing other problems, so I decided to figure out what was going on. Seems that the "types" field in package.json is not respected when using "exports". Luckily as of typescript 4.7, "exports" itself supports "types" fields for each declaration as well (see here).

Now, my app is using type: "module" so I'm not sure if this will work with the CJS import as well but I assume it will (if someone could check that would be great).

After adding this fix my types now work with no hacks 💥

[mattvague]

I believe this addresses #2506 as well

[josdejong]

Wow, that makes a lot of sense indeed. Thanks for figuring this out!