[New] TypeScript config: add .cts and .mts extensions

[Zamiell]

This PR is pretty self explanatory.
.cts and .mts are common file extensions used in projects that are not fully CJS or not fully ESM.
So I added those to the config.
I also fixed some of the grammar and made the comments wrap to 100 characters.

[ljharb]

Seems reasonable.

[ljharb]

I'll rebase and land this once we get more travis-ci credits.

[JounQin]

AFAIK, .cjs/.cts and .mjs/.mts must be used specifically, what means 'import/extensions': allExtensions is wrong configed now. import './x' should not try to resolve ./x.cts/.x.mts at all.

[ljharb]

@JounQin is that always? or only when verbatimModuleSyntax: true?

[JounQin]

@ljharb I don't think it's the same thing here.

[ljharb]

With TS transpiled to CJS, i would expect extensions to be looked up.

[JounQin]

No, the output extension will not change, although this feature is requested for a long time. TypeScript focuses on typings with correct module resolution, but never changes user's source codes.

[ljharb]

Gotcha. Does that mean this PR should be reverted? If it's not that straightforward, a PR to fix it would be appreciated.

[JounQin]

Yes, it must be reverted, I'll raise a PR tomorrow.

Hope you can pin me with TypeScript related changes next time. 🩷

[ljharb]

That's very reasonable; will do.