Separate `check-private-items` configuration for different lints

Description

Issue

check-private-items currently controls behavior of multiple lints, e.g. missing_panics_doc and missing_safety_doc.

However, I would like to check even private items for safety docs but I don't care as much about panics. Especially since we also lint tests where I often use panics.

Proposal

Add more fine-grained options which can override check-private-items:

• check-private-items-missing-panics-doc
• check-private-items-missing-safety-doc
• ... possibly more

Then clippy.toml such as

check-private-items = false
check-private-items-missing-safety-doc = true

would work like this:

#![warn(missing_panics_doc)]
#![warn(missing_safety_doc)]

// This would be warned against because of `missing_safety_doc`
unsafe fn private_unsafe_fun() {}

// This would be warned against because of `missing_panics_doc`
pub fn public_panicking_fun() { panic!(); }

// This would not be warned against because it's a panic inside a private function
fn private_panicking_fun() { panic!(); }

Version

No response

Additional Labels

@rustbot label +C-enhancement

Start by tracing how check-private-items is handled for the missing_panics_doc and missing_safety_doc lints. Determine how per-lint configuration should override the shared option, then verify that the proposed settings distinguish private safety documentation from private panic documentation.