Allow entering a reason for self-deletion

[cellio]

https://meta.codidact.com/questions/276801

When you delete your own post, it would be helpful to be able to indicate why -- you realized your answer is wrong, you decided based on feedback that it's not valuable, etc. The linked post suggests either a menu or a freeform textbox. I favor the latter, like for edits, but we'll need to figure out how to inject it. (Modal after you click "delete", and then you have to click something else to complete the deletion?)

[Trilarion]

In the UI it could be realized like flagging where you can give details which is afterwards transformed into part of the delete notice.

[cellio]

If we take the flag approach then we need to come up with some baked-in reasons. We're already showing a modal dialogue that people have to click "ok" on; can we add it there? Something like this (but with more space and the buttons moved down):

[Trilarion]

This should not be a big problem. It's more or less equivalent to the existing dialog which allows flagging.

What baked-in reasons would be reasonable? Are they really necessary?

In the past I have deleted own questions because: a) they were marked as duplicates, I agreed and found my question not to be adding any value, b) I found the post doesn't make much sense anymore at all or c) I found the post to be off-topic and possible wanted to re-create at another place (including accidentally posting at a wrong community).

[cellio]

I don't know if baked-in reasons are necessary; I'd rather start with just a textbox and see what patterns arise. And I definitely don't want people to have to go through two modals to delete a post, so it should all be in one, however it's implemented.

Right now, if you click the "delete" link you get the "are you sure?" modal. I'm proposing that we add a textbox for an optional delete reason to that modal, and then if it's populated, add it to the "deleted by so-and-so" notice that deleted posts have. Something like "...for the following reason: (text)".