Permit configuring the verbosity of error type `Display` impls

Once #1298 lands, the `Display` impls for error types will have behavior which changes based on `#[cfg(debug_assertions)]`: when it is disabled, error messages will be minimal, and when it is enabled, error messages will contain verbose but potentially-sensitive information.

Some users may want the ability to directly override this behavior (ie, set the verbosity directly rather than based on `#[cfg(debug_assertions)]`).