createCache with revalidateOnFocus does not work

[origin-master]

Bug report

Description / Observed Behavior

Custom cache settings in 1.0.0-beta.8 disables revalidateOnFocus behaviour; focus and visibilitychange events are not revalidating SWR caches.

Expected Behavior

Revalidate on focus on revalidateOnFocus: true, as non-cache version does.

Repro Steps / Code Example

CodePen: https://codepen.io/origin-master/pen/WNjwgYy

Additional Context

SWR version: 1.0.0-beta.8

This can be a problem...

registerOnFocus called in only here, and it's based on defaultConfig.cache:

swr/src/use-swr.ts

Lines 49 to 62 in c677d04

	if (!IS_SERVER) {
	const [FOCUS_REVALIDATORS, RECONNECT_REVALIDATORS] = getGlobalState(
	defaultConfig.cache
	)
	const revalidate = (revalidators: Record<string, Revalidator[]>) => {
	if (!defaultConfig.isDocumentVisible() || !defaultConfig.isOnline()) return
	for (const key in revalidators) {
	if (revalidators[key][0]) revalidators[key][0]()
	}
	}
	defaultConfig.registerOnFocus(() => revalidate(FOCUS_REVALIDATORS))
	defaultConfig.registerOnReconnect(() => revalidate(RECONNECT_REVALIDATORS))
	}

Current API encourages only cache from createCache(...) should be put into SWRConfig, and doesn't cares mutate:

const { cache, mutate } = createCache(new Map());
const Config = () => <SWRConfig value={{ cache }} />