Add ide-assist: replace_if_matches_to_if_let

[A4-Tacks]

Replace matches!() to let-chain in if condition.

Example

fn foo(x: Option<i32>) {
    if let Some(n) = x && $0matches!(n.checked_div(2), Some(5..8)) {
    }
}

->

fn foo(x: Option<i32>) {
    if let Some(n) = x && let Some(5..8) = n.checked_div(2) {
    }
}