Rollup merge of #144376 - estebank:issue-143795, r=lcnr

Suggest unwrapping when private method name is available in inner type

Given

```rust
fn main() {
    let maybe_vec = Some(vec![1,2,3]);
    assert_eq!(maybe_vec.len(), 3);
}
```

suggest unwraping `maybe_vec` to call `.len()` on the `Vec<_>`.

```
error[E0624]: method `len` is private
  --> $DIR/enum-method-probe.rs:61:9
   |
LL |     res.len();
   |         ^^^ private method
  --> $SRC_DIR/core/src/option.rs:LL:COL
   |
   = note: private method defined here
   |
note: the method `len` exists on the type `Vec<{integer}>`
  --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
help: consider using `Option::expect` to unwrap the `Vec<{integer}>` value, panicking if the value is an `Option::None`
   |
LL |     res.expect("REASON").len();
   |        +++++++++++++++++
```

When a method isn't available, we emit E0599, but when it is private we emit E0624. We now just invoke the same suggestion logic from the later that we already did in the former.

Fix rust-lang/rust#143795.

Author: matthiaskrgr