Add docs addressing "$attrs no longer contains events declared in the emits option" issue

[stevebauman]

Description of Problem

There is a long-standing discussion from 2021 with comments as recent as September 6th on the disappearance of event listeners in $attrs when those events are declared in the emits property:

vuejs/rfcs#397

This is documented here, but with no solution proposed:

https://vuejs.org/api/options-state.html#emits

Proposed Solution

Additional docs can be added for those who discover that this occurs so that developers can properly utilize this un-documented functionality in Vue (or, if the docs do exist, correct me if I'm wrong) that allows developers to create props for these event listeners that Vue will auto-populate if they conform to a specific naming convention.

Additional Information

N/A

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[NataliaTepluhina]

@stevebauman

If we want to add this part of the documentation, let's start with why do we want/need to check on the event. Otherwise the use-case is not clear (I know there are examples in the thread, but we need some "you might find yourself in a need to check for a listener bound).

[stevebauman]

@NataliaTepluhina Ok sounds good! Would you be able to share an example of the style you may be looking for from an existing doc page so I can write it in the format that you may be expecting? 🙏

The existing docs on this API page don't share any "why"'s, only "how"'s...

[NataliaTepluhina]

@stevebauman a good example can be a beginning of the Forms section in the Guide: https://vuejs.org/guide/essentials/forms.html - we show first how we could do it with our "known" tools and then introduce v-model. Here, we could say that "there might be a case where you need to know about passed listeners (case example)" and then proceed with explaining how. Personally, I never had the need to check for the existing listener so you might need to come with "real" example yourself

[stevebauman]

Ok thanks @NataliaTepluhina! Marking as draft and will update this a few hours (away from computer atm) and will mark ready once good to go for re-review.