improve [`almost_swapped`] to look for let statement

[DevAccentor]

fix #8151

improve [almost_swapped] to also detects code using let statements like

let b = 1;
let a = b;
let b = a;

let mut b = 1;
let a = b;
b = a;

changelog: improve [almost_swapped] to look for code using let statement

[rust-highfive]

r? @flip1995

(rust-highfive has picked a reviewer for you, use r? to override)

[Jarcho]

It would be better to rework this to parse the two statement into (Symbol|Expr, Expr) pairs and then check if it's almost swapped. Something like:

fn parse(...) -> Option<(ExprOrLocal, Expr)> { ... }

if let Some((lhs0, rhs0)) = parse(stmt[0])
    && let Some((lhs1, rhs1)) = parse(stmt[1])
    && is_same(lhs0, rhs1)
    && is_same(lhs1, rhs0)
{ ... }

[flip1995]

I like the suggestion by @Jarcho. This makes the code more DRY. Can you refactor the code please?

[flip1995]

Because I took too long for my review, I think this PR is stale, so I close it for now. @DevAccentor if you want to continue working on it, let me know and I'll reopen the PR. Sorry for not responding for so long!

[chansuke]

I would like to take over this PR.