suggest calling Self::associated_function()

[qutesy]

Given the following code: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=72d0a7426f82aeca7615c923eb4d2da4

struct S;

impl S {
    fn helper() {}

    fn doer(&self) {
        helper();
    }
}

The current output is:

Compiling playground v0.0.1 (/playground)
error[[E0425]](https://doc.rust-lang.org/stable/error-index.html#E0425): cannot find function `helper` in this scope
 [--> src/lib.rs:7:9
](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=72d0a7426f82aeca7615c923eb4d2da4#)  |
7 |         helper();
  |         ^^^^^^ not found in this scope

For more information about this error, try `rustc --explain E0425`.
error: could not compile `playground` due to previous error

Ideally the output should look like:

Consider calling the associated function `Self::helper()`.