Lint more cases with ptr_eq

[samueltardieu]

This PR:

• lints more case of raw pointer comparisons
• do not omit the named function to raw pointer conversion before suggesting
• trigger the ptr_eq lint only if cmp_null doesn't trigger first, as this is a more specialized version
• lints against != in addition to ==

The ptr_eq code has been moved from under operators to ptr.rs, in order to benefit from factorization.

Fix #14337

changelog: [ptr_eq]: handle more cases

[rustbot]

r? @Manishearth

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[samueltardieu]

The merge error seems unrelated:

Running linkchecker on "linkcheck/clippy"...
error: toolchain 'nightly-2025-02-27-x86_64-unknown-linux-gnu' is not installed
help: run `rustup toolchain install nightly-2025-02-27-x86_64-unknown-linux-gnu` to install it

@Manishearth Could you retry it?

[smoelius]

@samueltardieu Do you have reason to believe it will succeed?

That error seems to have popped up in a few places, e.g.:

• https://github.com/rust-lang/rust-clippy/actions/runs/13634343890/job/38109286686?pr=13718#step:7:46
• https://github.com/rust-lang/rust-clippy/actions/runs/13637211669/job/38118821217?pr=13931#step:7:45

EDIT: I haven't figured out what wants that particular nightly toolchain or why.

[lapla-cogito]

I don't think simply retrying will work, because this job has been consistently failing with the same error lately.
https://github.com/rust-lang/rust-clippy/actions/workflows/remark.yml

I'm taking a closer look, but I'm still trying to figure out the cause.

[samueltardieu]

Thanks @lapla-cogito, I am on my phone and did not see that other job failed as well.