types: add contextSeparator also on v4 t types

[marcalexiei]

I just noticed there is a separate t type function file for typescript@4.
I added #2017 patch to that file.

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• run tests npm run test
• tests are included
• commit message and code follows the Developer's Certification of Origin

[coveralls]

coverage: 92.36%. remained the same when pulling 6cab670 on marcalexiei:feature/type-custom-separator-on-ts4 into 181dcbd on i18next:master.

[adrai]

grazie ;-) => v23.4.4