Improve check-cfg CLI errors with more structured diagnostics

[Urgau]

This PR improve check-cfg CLI errors with more structured diagnostics.

In particular it now shows the statement where the error occurred, what kind lit it is, as well as pointing users to the doc for more details.

@rustbot label +F-check-cfg

[rustbot]

r? @nnethercote

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[rustbot]

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[bors]

☔ The latest upstream changes (presumably #124345) made this pull request unmergeable. Please resolve the merge conflicts.

[nnethercote]

r=me after rebasing.

[Urgau]

@nnethercote I believe I did two days ago. At least rebasing locally doesn't give any conflict.

But anyway, rebased and push.

[nnethercote]

Ah, yep.

@bors r+

[bors]

📌 Commit 228496e has been approved by nnethercote

It is now in the queue for this repository.

[bors]

⌛ Testing commit 228496e with merge 69f53f5...

[bors]

☀️ Test successful - checks-actions
Approved by: nnethercote
Pushing 69f53f5 to master...

[rust-timer]

Finished benchmarking commit (69f53f5): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

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Bootstrap: 674.088s -> 674.594s (0.08%)
Artifact size: 315.91 MiB -> 315.87 MiB (-0.01%)