dillon1000/react

Attach Listeners Eagerly to Roots and Portal Containers (#19659)

* Failing test for #19608

* Attach Listeners Eagerly to Roots and Portal Containers

* Forbid createEventHandle with custom events

We can't support this without adding more complexity. It's not clear that this is even desirable, as none of our existing use cases need custom events. This API primarily exists as a deprecation strategy for Flare, so I don't think it is important to expand its support beyond what Flare replacement code currently needs. We can later revisit it with a better understanding of the eager/lazy tradeoff but for now let's remove the inconsistency.

* Reduce risk by changing condition only under the flag

Co-authored-by: koba04 <[email protected]>