Add lint to detect unnecessary `clone()` for `AsRef`-taking function

What it does

Consider this code:

use std::path::*;

fn item(_x: impl AsRef<Path>) {}

pub fn work(x: PathBuf) {
    item(x.clone()); // unnecessary clone
    item(&x);
}

This should be better written as

use std::path::*;

fn item(_x: impl AsRef<Path>) {}

pub fn work(x: PathBuf) {
    item(&x);
    item(&x);
}

Clippy as a bunch of lints against unnecessary borrowing, which is syntactic noise but ultimately usually harmless. Unnecessary cloning however can make the program slower for no good reason, so it is IMO quite relevant to lint against as well.

Clippy is already able to detect similar cases, like unnecessary to_owned():

use std::path::*;

fn item(_x: impl AsRef<Path>) {}

pub fn work(x: &Path) {
    item(x.to_owned()); // clippy lints here
    item(x);
}

Advantage

Same as the existing unnecessary_to_owned: avoids unnecessary copies and function calls, making the code both less noisy and faster.

Drawbacks

If it can be implemented without false positivies, I cannot think of any drawbacks.

Example

(see description above)

Start by locating the existing unnecessary_to_owned lint, since the issue identifies it as a similar case. Compare its implementation and tests with the proposed clone() pattern, then define coverage and false-positive cases for functions taking AsRef; done means the examples are linted without incorrect suggestions and the relevant tests pass.