fix: export IcuTrans and add typescript definitions and tests

[cellog]

for issue #1869

I neglected to add typescript types or tests for typescript and also neglected to export the IcuTrans component. This fixes that oversight

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

Checklist (for documentation change)

• only relevant documentation part is changed (make a diff before you submit the PR)
• motivation/reason is provided
• commit message and code follows the Developer's Certification of Origin

[coveralls]

coverage: 97.593%. remained the same
when pulling 7167741 on cellog:issue-1869-export-icu-trans
into 280bbee on i18next:master.

[adrai]

included in v16.1.1