Get All Files With A Certain Extension Recursively In Rust

```cargo
[package]
edition = "2021"
[dependencies]
walkdir = "2"
```

use std::path::PathBuf;
use walkdir::WalkDir;

fn main() {
    let files = get_files_in_dir_matching_extension_recursively(
        "recursive_test/example", vec!["txt"]
    );
    dbg!(files);
}

fn get_files_in_dir_matching_extension_recursively(dir: &str, exts: Vec<&str>) -> Vec<PathBuf> {
    WalkDir::new(dir)
        .into_iter()
        .filter(|e| 
            match e.as_ref().unwrap().path().extension() {
                Some(x) => exts.contains(&x.to_str().unwrap()),
                None => false
    }).map(|e| e.unwrap().into_path()).collect()
}