Fix ICE in transmutability error reporting when type aliases are normalized
Fixesrust-lang/rust#151462
Transmutability error reporting hit an ICE when type aliases were normalized for diagnostics. For example, when type
`JustUnit = ()` normalizes to `()`, the check passes unexpectedly even though the original check with `JustUnit` failed.
Fixed by adding a retry in the `Answer::Yes` arm that checks with the root obligation's types before panicking. The retry only occurs when the root obligation differs and is a Transmute trait predicate.
Also added a test that reproduces the original ICE.
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