The compiler will now issue a warning for crates that have syntax of the form
`extern crate "foo" as bar`, but it will still continue to accept this syntax.
Additionally, the string `foo-bar` will match the crate name `foo_bar` to assist
in the transition period as well.
This patch will land hopefully in tandem with a Cargo patch that will start
translating all crate names to have underscores instead of hyphens.
cc #23533
