discriminant value on non-field-less enum should highlight variant with field

[pnkfelix]

While reviewing PR #60732, I noticed that both the current stderr for test cases like tag-variant-disr-non-nullary.stderr highlights a bunch of variants that all have no fields on them.

This is confusing, because the diagnostic is complaining that you can only use this feature on enums without fields, but the diagnostic is showing you only cases without fields. Ideally it would include both the explicit discriminator value and some variant of the enum that has fields on it. For example, in the case linked above, it would also highlight the variant on this line:

rust/src/test/ui/parser/tag-variant-disr-non-nullary.rs

Line 8 in 37ff5d3

Other(usize),

(Arguably if rust-lang/rfcs#2363 (#60553) gets implemented and stabilized quickly, the diagnostic being criticized here will go away, and my suggestion will be pointless. But I suspect this would be an easy change to make that would make life easier for some developers.)