Replace all sort with unstable sort (#38427)

["When applicable, unstable sorting is preferred because it is generally
faster than stable sorting and it doesn’t allocate auxiliary
memory."](https://doc.rust-lang.org/std/vec/struct.Vec.html#method.sort)

Binary also reduced by 1KB in Release.

Testing: No behaviour change as semantically all current usage does not
have any pair with `std::cmp::Ordering::Equal`.

Signed-off-by: Euclid Ye <euclid.ye@huawei.com>

ports/servoshell/desktop/app.rs

@@ -814,7 +814,7 @@ fn load_userscripts(userscripts_directory: Option<&Path>) -> std::io::Result<Vec
         let mut files = std::fs::read_dir(userscripts_directory)?
             .map(|e| e.map(|entry| entry.path()))
             .collect::<Result<Vec<_>, _>>()?;
-        files.sort();
+        files.sort_unstable();
         for file in files {
             userscripts.push(UserScript {
                 script: std::fs::read_to_string(&file)?,