unwrap_in_result: allow unwrapping infallible result type

[zihan0822]

fixes #16709

changelog: [unwrap_in_result]: allow unwrapping infallible result type

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[github-actions]

Lintcheck changes for c8dab51

Lint	Added	Removed	Changed
clippy::unwrap_in_result	0	4	1

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[samueltardieu]

Related: #16712

The current test is too naive. If #16712 is merged first, you should use is_visibly_uninhabited instead of is_never_like.

[themavik]

Renaming to is_option_or_fallible_result and bailing when is_never_like sees an uninhabited Err matches Result<T, Infallible> ergonomics. If the is_never_like -> is_visibly_uninhabited refactor in related PRs lands, mirror that predicate here so structurally empty errors stay aligned.

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[rustbot]

☔ The latest upstream changes (possibly #17607) made this pull request unmergeable. Please resolve the merge conflicts.