vec -> array lint for simple cases

In many blog posts online I see code like:

fn main() {
    let a = vec![10, 20, 30];
    let tot: u32 = a.iter().sum();
    println!("Total: {}", tot);
}

I'd like a Clippy lint that suggests to write instead:

fn main() {
    let a = [10, 20, 30];
    let tot: u32 = a.iter().sum();
    println!("Total: {}", tot);
}

That is, to suggest to use arrays in simple cases where dynamic arrays aren't necessary. Even if such lint is very conservative it's still going to be useful to teach inexperienced Rust programmers to avoid heap allocations (Clippy is also a learning tool today). Rust programmers later could remember the idea and generalize it.

The issue names no implementation files, tests, or entry points. Start by locating Clippy's lint and test conventions, then define conservative cases based on the vec! and array examples; done means those simple cases receive a tested suggestion without affecting cases that need dynamic allocation.