## Summary
Set up the experiment to migrate event dispatching in the React Native
renderer to be based on the native EventTarget API.
Behind the `enableNativeEventTargetEventDispatching` flag, events are
dispatched through `dispatchTrustedEvent` instead of the legacy plugin
system.
Regular event handler props are NOT registered via addEventListener at
commit time. Instead, a hook on EventTarget
(`EVENT_TARGET_GET_DECLARATIVE_LISTENER_KEY`) extracts handlers from
`canonical.currentProps` at dispatch time, shifting cost from every
render to only when events fire. The hook is overridden in
ReactNativeElement to look up the prop name via a reverse mapping from
event names (built lazily from the view config registry).
Responder events bypass EventTarget entirely. `negotiateResponder` walks
the fiber tree directly (capture then bubble phase), calling handlers
from `canonical.currentProps` and checking return values inline.
Lifecycle events (`responderGrant`, `responderMove`, etc.) call handlers
directly from props and inspect return values — `onResponderGrant`
returning `true` blocks native responder,
`onResponderTerminationRequest` returning `false` refuses termination.
This eliminates all commit-time cost for responder events (no wrappers,
no addEventListener, no `responderWrappers` on canonical).
## How did you test this change?
Flow
Tested e2e in RN using Fantom tests (that will land after this).
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