Detects if/else chains with redundant conditions

What it does

Detects when the if condition of if/else chains are redundant or if a part of the chain will never execute.

Advantage

This type of code represents likely a bug in either the condition, or allows for an entire if/else arm to be removed.

Drawbacks

Implementation complexity? For numeric types and comparisons, this would be easy to implement, for other types not so much.

Example

fn main() {
    let x = 42;
    if x > 10 {
        println!("1");
    } else if x == 42 { // This will always be true if the above is true, and will always be false if the above is false
        println!("2"); // unreachable code
    }
}

fn main() {
    let x = 42;
    if x > 10 {
        println!("1");
    } else if true {
        if x > 10 {
            println!("2"); // unreachable code
        }
    }
}

Start with the two Rust examples in the issue and define the expected diagnostics for redundant conditions and unreachable if/else arms. The issue names no source files, tests, or entry points, so locating a comparable Clippy lint and its tests is required before implementation. Done means the specified cases are detected without overreaching into unsupported condition types.