Rollup merge of #100479 - compiler-errors:argument-type-error-improvements, r=lcnr

Argument type error improvements

Motivated by this interesting code snippet:

```rust
#[derive(Copy, Clone)]
struct Wrapper<T>(T);

fn foo(_: fn(i32), _: Wrapper<i32>) {}

fn f(_: u32) {}

fn main() {
    let w = Wrapper::<isize>(1isize);
    foo(f, w);
}
```

Which currently errors like:
```
error[E0308]: arguments to this function are incorrect
  --> src/main.rs:10:5
   |
10 |     foo(f, w);
   |     ^^^ -  - expected `i32`, found `isize`
   |         |
   |         expected `i32`, found `u32`
   |
   = note: expected fn pointer `fn(i32)`
                 found fn item `fn(u32) {f}`
   = note: expected struct `Wrapper<i32>`
              found struct `Wrapper<isize>`
note: function defined here
  --> src/main.rs:4:4
   |
4  | fn foo(_: fn(i32), _: Wrapper<i32>) {}
   |    ^^^ ----------  ---------------
```

Specifically, that double `expected .. found ..` which is very difficult to correlate to the types in the arguments. Also, the fact that "expected `i32`, found `isize`" and the other argument mismatch label don't even really explain what's going on here.

After this PR:
```
error[E0308]: arguments to this function are incorrect
  --> $DIR/two-mismatch-notes.rs:10:5
   |
LL |     foo(f, w);
   |     ^^^
   |
note: expected fn pointer, found fn item
  --> $DIR/two-mismatch-notes.rs:10:9
   |
LL |     foo(f, w);
   |         ^
   = note: expected fn pointer `fn(i32)`
                 found fn item `fn(u32) {f}`
note: expected struct `Wrapper`, found a different struct `Wrapper`
  --> $DIR/two-mismatch-notes.rs:10:12
   |
LL |     foo(f, w);
   |            ^
   = note: expected struct `Wrapper<i32>`
              found struct `Wrapper<isize>`
note: function defined here
  --> $DIR/two-mismatch-notes.rs:4:4
   |
LL | fn foo(_: fn(i32), _: Wrapper<i32>) {}
   |    ^^^ ----------  ---------------

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
```

Yeah, it's a bit verbose, but much clearer IMO.

---

Open to discussions about how this could be further improved. Motivated by `@jyn514's` [tweet](https://mobile.twitter.com/joshuayn514/status/1558042020601634816) here.

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