export event hint type from browser

[vcanales]

Before submitting a pull request, please take a look at our
Contributing guidelines and verify:

• If you've added code that should be tested, please add tests.
• Ensure your code lints and the test suite passes (yarn lint) & (yarn test).

---

EventHint type is missing from the exported types; required to properly declare, for instance, a beforeSend callback.

[HazAT]

Thx