Bring documentation of Path::to_path_buf in line with the rest of Path/PathBuf

Changes the example from using the qualified path of PathBuf with an import. This is what's done in all other Path/PathBuf examples and makes the code look a bit cleaner.

library/std/src/path.rs

@@ -2143,10 +2143,10 @@ pub fn to_string_lossy(&self) -> Cow<'_, str> {
     /// # Examples
     ///
     /// ```
-    /// use std::path::Path;
+    /// use std::path::{Path, PathBuf};
     ///
     /// let path_buf = Path::new("foo.txt").to_path_buf();
-    /// assert_eq!(path_buf, std::path::PathBuf::from("foo.txt"));
+    /// assert_eq!(path_buf, PathBuf::from("foo.txt"));
     /// ```
     #[rustc_conversion_suggestion]
     #[must_use = "this returns the result of the operation, \