improve use of `ErrorGuaranteed`

[lcnr]

there are multiple small things to improve ErrorGuaranteed:

• remove https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.DelaySpanBugEmitted.html and always use ErrorGuaranteed directly.
• add a way to create a ty_error and const_error by using an existing ErrorGuaranteed instead of using another delay_span_bug.
• change uses of references_error which use delay_span_bug right after to instead use TypeVisitable::error_reported() and not emit a span_bug.
• in TypeVisitable::error_reported(), instead of using ErrorGuaranteed::unchecked_claim_error_was_emitted(), use the tls tcx to check that tcx.sess.has_errors() is true (maybe in a #[cold] nested function for perf).
• change error_reported to use Result<(), ErrorGuaranteed> instead of an option
• consider merging error_reported and references_error so that there's only 1 function, using .is_ok() in the current uses of references_error. Not sure about this point, might not make stuff clearer and I can't think of a good name.

[chenyukang]

@rustbot claim

[chenyukang]

The last sub-item didn't implemented.

[lcnr]

👍