Suggest `ptr::null()` over `ptr::null_mut()` if the receiver takes `*const`

I'm often passing null pointers for optional arguments when doing C FFI. Some functions take *mut as argument, others *const. Since mutable pointers coerce to const pointers, I can call a function taking a *const argument by accidentally passing in ptr::null_mut(), where the more correct usage would be to pass ptr::null().

Example:

use std::ptr;

fn foo(arg: *const u32) {}

fn main() {
    foo(ptr::null_mut());
}

Here I would like Clippy to suggest calling foo with ptr::null() instead.

Start by reproducing the Rust example with Clippy, then locate the lint implementation and its tests for pointer arguments. Done means Clippy detects ptr::null_mut() passed to a *const parameter and suggests ptr::null(), while leaving *mut parameters unchanged.