[Use Case]: scope based normalization of const generics

[BoxyUwU]

Code description

fn concrete(input: [u32; 10]) {
    // ...
}

fn generic<const N: usize>(input: [u32; N]) {
    match N {
        10 => concrete(input),
        _ => panic!("invalid input size"),
    }
}

Some people have wanted this to compile, this has some overlap with pattern types I expect cc @oli-obk

[jyn514]

this looks like type flow analysis: https://www.typescriptlang.org/docs/handbook/2/narrowing.html