util: refactor filterDuplicateStrings for readability

Modernize filterDuplicateStrings by using for-of loop and ternary
operator for cleaner, more idiomatic ES2018 code.

Changes:
- Replace traditional for loop with for-of iteration
- Consolidate conditional map.set() using ternary operator
- Eliminate iterator variable reducing cognitive complexity

No functional changes, performance remains equivalent.

Author: Ayoub-Mabrouk

lib/internal/util.js

@@ -326,14 +326,9 @@ function emitExperimentalWarning(feature, messagePrefix, code, ctor) {
 
 function filterDuplicateStrings(items, low) {
   const map = new SafeMap();
-  for (let i = 0; i < items.length; i++) {
-    const item = items[i];
+  for (const item of items) {
     const key = StringPrototypeToLowerCase(item);
-    if (low) {
-      map.set(key, key);
-    } else {
-      map.set(key, item);
-    }
+    map.set(key, low ? key : item);
   }
   return ArrayPrototypeSort(ArrayFrom(map.values()));
 }