Explicit return type not required in TypeScript anymore

[mofojed]

Description

Not sure when this changed, but we used to enforce an explicit return type. We're no longer doing that, and we should re-enable enforcing it it.

Steps to reproduce

1. In the code, remove the return type from a function

Expected results

1. Linter should fail, requiring a return type to be specified

Actual results

1. Linter does not fail

[mattrunyon]

I think previously one of the configs we extended had explicit-module-boundary-types enabled. This is for anything exported and the benefit is it makes it more clear if a change was made to a potentially public facing API

There is also explicit-function-return-type which I don't think we had enabled. This requires it for all functions, even if they are not exported