Improve how `eventIDs` are created and propogated.

[AbhiPrasad]

Right now there's a lot of redundancy on how eventIDs are created and used. We can maybe simplify this to reduce bundle size.

hub.captureException first creates an eventID and passes it as a hint.

sentry-javascript/packages/hub/src/hub.ts

Line 188 in 1bf9883

const eventId = (this._lastEventId = hint && hint.event_id ? hint.event_id : uuid4());

This then calls client.captureException which grabs the eventID from the hint, passes that hint down, overwrites the eventID, and then returns that

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

Lines 115 to 126 in 9e87bf9

	let eventId: string | undefined = hint && hint.event_id;
	this._process(
	this._getBackend()
	.eventFromException(exception, hint)
	.then(event => this._captureEvent(event, hint, scope))
	.then(result => {
	eventId = result;
	}),
	);
	return eventId;

eventFromException sets the eventID on the event based on the hint

sentry-javascript/packages/browser/src/eventbuilder.ts

Lines 20 to 31 in 9e87bf9

	export function eventFromException(options: Options, exception: unknown, hint?: EventHint): PromiseLike<Event> {
	const syntheticException = (hint && hint.syntheticException) || undefined;
	const event = eventFromUnknownInput(exception, syntheticException, {
	attachStacktrace: options.attachStacktrace,
	});
	addExceptionMechanism(event); // defaults to { type: 'generic', handled: true }
	event.level = Severity.Error;
	if (hint && hint.event_id) {
	event.event_id = hint.event_id;
	}
	return resolvedSyncPromise(event);
	}

client._captureEvent returns the id on the event

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

Lines 499 to 509 in 9e87bf9

	protected _captureEvent(event: Event, hint?: EventHint, scope?: Scope): PromiseLike<string | undefined> {
	return this._processEvent(event, hint, scope).then(
	finalEvent => {
	return finalEvent.event_id;
	},
	reason => {
	logger.error(reason);
	return undefined;
	},
	);
	}

client._processEvent prepares the event:

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

Line 555 in 9e87bf9

return this._prepareEvent(event, scope, hint)

which grabs the event id from the event, the hint, or generates a new one.

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

Line 352 in 9e87bf9

event_id: event.event_id || (hint && hint.event_id ? hint.event_id : uuid4()),