Add code review suggestions.

Author: Isira-Seneviratne

extractor/src/main/java/org/schabi/newpipe/extractor/stream/SubtitlesStream.java

@@ -1,7 +1,5 @@
 package org.schabi.newpipe.extractor.stream;
 
-import static org.schabi.newpipe.extractor.utils.Utils.EMPTY_STRING;
-
 import org.schabi.newpipe.extractor.MediaFormat;
 import org.schabi.newpipe.extractor.services.youtube.ItagItem;
 import org.schabi.newpipe.extractor.utils.LocaleCompat;

extractor/src/main/java/org/schabi/newpipe/extractor/utils/LocaleCompat.java

@@ -2,15 +2,22 @@
 
 import java.util.Locale;
 
-public class LocaleCompat {
+/**
+ * This class contains a simple implementation of {@link Locale#forLanguageTag(String)} for Android
+ * API levels below 21 (Lollipop). This is needed as core library desugaring does not backport that
+ * method as of this writing.
+ *
+ * Relevant issue: https://issuetracker.google.com/issues/171182330
+ */
+public final class LocaleCompat {
     private LocaleCompat() {
     }
 
-    // Source: LocaleListCompat's private forLanguageTagCompat() method.
-    // Use Locale.forLanguageTag() on API level >= 21 instead.
+    // Source: The AndroidX LocaleListCompat class's private forLanguageTagCompat() method.
+    // Use Locale.forLanguageTag() on Android API level >= 21 / Java instead.
     public static Locale forLanguageTag(final String str) {
         if (str.contains("-")) {
-            String[] args = str.split("-", -1);
+            final String[] args = str.split("-", -1);
             if (args.length > 2) {
                 return new Locale(args[0], args[1], args[2]);
             } else if (args.length > 1) {
@@ -19,7 +26,7 @@ public static Locale forLanguageTag(final String str) {
                 return new Locale(args[0]);
             }
         } else if (str.contains("_")) {
-            String[] args = str.split("_", -1);
+            final String[] args = str.split("_", -1);
             if (args.length > 2) {
                 return new Locale(args[0], args[1], args[2]);
             } else if (args.length > 1) {