chore: refactor Jest configuration to allow verbatimModuleSyntax

[mrazauskas]

Fixes #27

For reference see TypeScript documentation:

With [the verbatimModuleSyntax] option, what you see is what you get.

That does have some implications when it comes to module interop though. Under this flag, ECMAScript imports and exports won’t be rewritten to require calls when your settings or file extension implied a different module system. Instead, you’ll get an error. If you need to emit code that uses require and module.exports, you’ll have to use TypeScript’s module syntax that predates ES2015

The syntax in this PR follows the one seen in the documentation. That is the change needed to allow verbatimModuleSyntax: true. If you really need it.

[mrazauskas]

Tests were failing in this package, because the extensionsToTreatAsEsm option was missing. I simply copied the options to make it similar to other files.

[mrazauskas]

Currently with "src/**/*.ts" no files are included and TS is complaining. Not sure what was the exact idea here. Perhaps "include": [] was intended?

[mrazauskas]

Looks like it does nothing in this setup.

[juanjoDiaz]

What's the difference between export default & export equals?

[mrazauskas]

See documentation of the verbatimModuleSyntax option (link was provided in the description):

[mrazauskas]

@juanjoDiaz One detail which might be important. I was playing with verbatimModuleSyntax: true in one projects which is using const enums and has preserveConstEnums: true. In my case I was expecting enum members to be inlined at use site, but noticed that tsc does not do this if verbatimModuleSyntax: true.

Might be this is something you would like to double check. Reference: microsoft/TypeScript#52669 (comment)