Handle unit struct with same name as field in pattern destructuring

[estebank]

Given the following code

struct foo;
struct Thing { foo: String }

fn example(t: Thing) {
    let Thing { foo } = t;
}

generate the following error

error[E0530]: let bindings cannot shadow tuple structs
 --> src/lib.rs:5:17
  |
1 | struct foo;
  | ------------- a unit struct `foo` is defined here
...
5 |     let Thing { foo } = t;
  |                 ^^^ cannot be named the same as a unit struct

instead of

error[E0308]: mismatched types
 --> src/lib.rs:5:17
  |
5 |     let Thing { foo } = t;
  |                 ^^^ expected struct `std::string::String`, found struct `foo`
  |
  = note: expected type `std::string::String`
             found type `foo`

[petrochenkov]

foo is not a binding in this case and it's indeed a type mismatch error.
It's probably not a good idea to give plain incorrect information in diagnostics.
Perhaps something like 765076f may be a better approach? I.e. explicitly telling that foo is not interpreted as a new binding.

[estebank]

@petrochenkov that's not a bad option. The proposed output is based on the output when writing struct foo(); instead.

[qnighy]

Related: #42876