Guidelines for must_use?

[scottmcm]

I got assigned a pr (rust-lang/rust#78202) to add this to something, and realized I didn't have a great sense of when something should or shouldn't be must_use -- in some ways most things could be.

Would be nice to have a checklist of things to consider.

This is especially true with must_use stable on functions now -- some people would like to put it on essentially everything, which seems like not what's desirable. I suppose guidelines on this could also push feedback up to lang to change the rules for it...

[m-ou-se]

cc rust-lang/rust#48926