events: add getMaxListeners method

[KhafraDev]

This adds an events.getMaxListeners method that both EventEmitter & EventTarget can use. Currently, there isn't a way to get the max listeners for an EventTarget.

Undici currently increases AbortSignal's max listeners because 10 is too conservative for fetch. However someone might increase this limit, which we override. Using this we can detect if the limit's been changed, and not set our own default if it has.

import { getMaxListeners, setMaxListeners } from 'node:events'

const { signal } = new AbortController()

getMaxListeners(signal) // 10
setMaxListeners(11, signal)
getMaxListeners(signal) // 11

Refs: nodejs/undici#1910 (comment)

[debadree25]

also cc'ing @nodejs/events

[debadree25]

I think this would qualify as semver-minor too? since adding a new api hence added the label