Emit a match-expression for Destructure nodes

This part of the current generated code would be better expressed as a `match`, which would be able to work equally well against enums later.

```rust
let __v3 = &__v0.x;
let __v4 = &__v0.y;
/* ... */
```

```rust
match __v0 {
    Point { x: __v3, y: __v4 } => {
        /* ... */
    }
}
```