Fix -x option behavior

This PR addresses an issue where `target_dirs` were being optimized out\
before being passed to the `get_filesystem_devices()` function.
The changes in this PR ensure that `target_dirs` are passed directly
to `get_filesystem_devices()`, and only then are they simplified.

Example of a command that currently doesn't work correctly:
```sh
dust -x $(findmnt -S tmpfs -o target -n)
```

It should show the usage of all tmpfs mounts, but it currently shows
just the the root mountpoints like `/run`, since all the mountpoints
nested under it are optimized out.

src/main.rs

@@ -192,10 +192,10 @@ fn main() {
     let limit_filesystem = options.get_flag("limit_filesystem");
     let follow_links = options.get_flag("dereference_links");
 
-    let simplified_dirs = simplify_dir_names(target_dirs);
     let allowed_filesystems = limit_filesystem
-        .then(|| get_filesystem_devices(simplified_dirs.iter()))
+        .then(|| get_filesystem_devices(target_dirs.iter().cloned()))
         .unwrap_or_default();
+    let simplified_dirs = simplify_dir_names(target_dirs);
 
     let ignored_full_path: HashSet<PathBuf> = ignore_directories
         .into_iter()

src/utils.rs

@@ -34,11 +34,12 @@ pub fn simplify_dir_names<P: AsRef<Path>>(filenames: Vec<P>) -> HashSet<PathBuf>
     top_level_names
 }
 
-pub fn get_filesystem_devices<'a, P: IntoIterator<Item = &'a PathBuf>>(paths: P) -> HashSet<u64> {
+pub fn get_filesystem_devices<'a, P: IntoIterator<Item = &'a str>>(paths: P) -> HashSet<u64> {
     // Gets the device ids for the filesystems which are used by the argument paths
     paths
         .into_iter()
-        .filter_map(|p| match get_metadata(p, false) {
+        .map(PathBuf::from)
+        .filter_map(|p| match get_metadata(&p, false) {
             Some((_size, Some((_id, dev)), _time)) => Some(dev),
             _ => None,
         })