Rethrow exceptions if promise is not yielded

[b-viguier]

It's very useful to launch an async function, and don't care about it's result/promise. But it can have a tricky side-effect, since exceptions will be stuck in the promise and never be propagated anywhere…

We could ensure that a "non yielded" promise will rethrow all exceptions when rejected.
See similar feature in Amp.

Notes 🤔 :

• What about rejected promises? They shouldn't throw an exception at creation…
• How to explicitly indicates that we don't care about exceptions for a particular promise? Is it easy to try/catch all?