Auto merge of #17571 - winstxnhdw:bool-to-enum-no-dupe, r=Veykril

feat: do not add new enum if it already exists

## Summary

This PR introduces a check for the existence of another enum within the current scope, and if it exist, we skip `add_enum_def`.

## Why?

Currently, when using the `bool_to_enum` assist more than once, it is possible to add multiple enum definitions. For example, the following snippet,

```rs
#[derive(PartialEq, Eq)]
enum Bool {
    True,
    False,
}

fn main() {
    let a = Bool::True;
    let b = true;
    println!("Hello, world!");
}
```

will be transformed into,

```rs
#[derive(PartialEq, Eq)]
enum Bool {
    True,
    False,
}

#[derive(PartialEq, Eq)]
enum Bool {
    True,
    False,
}

fn main() {
    let a = Bool::True;
    let b = Bool::True;
    println!("Hello, world!");
}
```

This can be annoying for users to clean up.

0 files changed, 0 insertions, 0 deletions