Rollup merge of #129101 - compiler-errors:deref-on-parent-by-ref, r=lcnr

Fix projections when parent capture is by-ref but child capture is by-value in the `ByMoveBody` pass

This fixes a somewhat strange bug where we build the incorrect MIR in #129074. This one is weird, but I don't expect it to actually matter in practice since it almost certainly results in a move error in borrowck. However, let's not ICE.

Given the code:

```
#![feature(async_closure)]

// NOT copy.
struct Ty;

fn hello(x: &Ty) {
    let c = async || {
        *x;
        //~^ ERROR cannot move out of `*x` which is behind a shared reference
    };
}

fn main() {}
```

The parent coroutine-closure captures `x: &Ty` by-ref, resulting in an upvar of `&&Ty`. The child coroutine captures `x` by-value, resulting in an upvar of `&Ty`. When constructing the by-move body for the coroutine-closure, we weren't applying an additional deref projection to convert the parent capture into the child capture, resulting in an type error in assignment, which is a validation ICE.

As I said above, this only occurs (AFAICT) in code that eventually results in an error, because it is only triggered by HIR that attempts to move a non-copy value out of a ref. This doesn't occur if `Ty` is `Copy`, since we'd instead capture `x` by-ref in the child coroutine.

Fixes #129074

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