Lint option: Highlighting copies

It would be nice to have a lint feature that, when enabled, will highlight all instances where a variable is copied. This would be useful because it's not always clear when a copy would occur, and highlighting copies could point out areas where code compiles correctly, but could be written better.

For example:

#[derive(Debug, Clone, Copy)]
struct Test {
    num: [u8; 20],
}

fn func(_: Test) {
    // ...
}

fn main() {
    let t = Test{
        num:[0;20],
    };
    let t2 = t.clone();
    func(t);
    println!("{:?}", t2);
}

In this case, the author of the code is unaware that Test implements Copy, so they clone t to pass to func() in order to keep using t after they assume it was moved. When highlighting is enabled, the t in func(t) would be highlighted which would provide a visual indicator that the clone is unnecessary, as t will be copied instead of moved when passed to func.

Start by examining rust-analyzer's existing lint and highlighting behavior, then trace how the Rust example's Copy semantics are represented. Define the enabled-option scope and how copied variable uses should be identified and highlighted, and add coverage for the provided Test example before verifying the resulting editor highlighting.