manual_let_else: support struct patterns
This adds upon the improvements of #10797 and:
* Only prints `()` around `Or` patterns at the top level (fixing a regression of #10797)
* Supports multi-binding patterns: `let (u, v) = if let (Some(u_i), Ok(v_i)) = ex { (u_i, v_i) } else ...`
* Traverses through tuple patterns: `let v = if let (Some(v), None) = ex { v } else ...`
* Supports struct patterns: `let v = if let S { v, w, } = ex { (v, w) } else ...`
```
changelog: [`manual_let_else`]: improve pattern printing to support struct patterns
```
fixes#10708fixes#10424
2490de476a