Re-opening deprecating Option::unwrap and Result::unwrap

CAD97:

There's a secondary argument that calling it assert! leans too much into Try/? being a "truthy"/"falsey" distinction, but the counterargument would be that the shape already exists anyway, and that defining assert in terms of ControlFlow::Continue vs Break still makes sense.

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I'd say that what you'd really want is

impl<T, E> Result<T, E> {
   fn assert_ok(self) -> T;
   fn assert_err(self) -> E;
}

impl<T> Option<T> {
   fn assert_some(self) -> T;
   fn assert_none();
}

It would be nice if those could be postfix macros which even allowed something like

let f = foo().assert_ok!("nice message {}", "with formatting");

or even

let f = bar().assert_ok!(err => "the error code was {}", err.code);