fix(core): Respect event.event_id in scope.captureEvent return value

[limbonaut]

I found a bug while working on the JavaScript SDK integration in Sentry for Godot (it's a game engine SDK).

When you call Sentry.captureEvent({ event_id: "<custom-event-id>" }), the event_id you provide IS actually used when the event is processed and sent to Sentry (because prepareEvent.ts correctly checks event.event_id first). However, the return value from captureEvent() is wrong because:

In sentry-javascript/packages/core/src/scope.ts:

sentry-javascript/packages/core/src/scope.ts

Line 758 in 170b6f8

const eventId = hint?.event_id || uuid4();

This only checks hint?.event_id, not event.event_id. So while your supplied event_id gets sent to Sentry correctly, the function returns a newly generated UUID.

Closes #issue_link_here