New lint: unused underscore prefixed argument

[clueless-skywatcher]

• Followed [lint naming conventions][lint_naming]
• Added passing UI tests (including committed .stderr file)
• cargo test passes locally
• Executed cargo dev update_lints
• Added lint documentation
• Run cargo dev fmt

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changelog: [unused_underscore_prefixed_argument]: add lint

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[github-actions]

Lintcheck changes for 926c9f2

Lint	Added	Removed	Changed
clippy::unused_underscore_prefixed_argument	161	0	0

This comment will be updated if you push new changes

[DanielEScherzer]

Community review: the second new added report given in lintcheck is for https://docs.rs/backtrace/0.3.73/src/backtrace/symbolize/gimli/libs_dl_iterate_phdr.rs.html#42 - this exactly highlights what I was warned about: the signature of the function comes from being passed as a pointer to https://docs.rs/libc/0.2.186/libc/fn.dl_iterate_phdr.html

a few reports later is https://docs.rs/bytes/1.6.1/src/bytes/bytes.rs.html#1146 - this signature comes from being stored in a function pointer field, https://docs.rs/bytes/1.6.1/src/bytes/bytes.rs.html#118

I didn't check all of the hits, but at least some of these are places where the lint is problematic

Maybe start by excluding anything marked as extern ?

View changes since this review

[rustbot]

☔ The latest upstream changes (possibly #17385) made this pull request unmergeable. Please resolve the merge conflicts.