Add language normalization for "arb" (Standard Arabic)

This is an individual language (ISO 639-3) part of the Arabic
macrolanguage ("ar" in ISO 639-1). Add this mapping to our
existing list similar to other individual to macrolanguage
mappings we have already.

Issue: Issue: google/ExoPlayer#10255
PiperOrigin-RevId: 448911950

library/common/src/main/java/com/google/android/exoplayer2/util/Util.java

@@ -2719,6 +2719,7 @@ public final class Util {
         "ji", "yi",
         // Individual macrolanguage codes mapped back to full macrolanguage code.
         // See https://en.wikipedia.org/wiki/ISO_639_macrolanguage
+        "arb", "ar-arb",
         "in", "ms-ind",
         "ind", "ms-ind",
         "nb", "no-nob",

library/common/src/test/java/com/google/android/exoplayer2/util/UtilTest.java

@@ -1162,6 +1162,7 @@ public class UtilTest {
     assertThat(Util.normalizeLanguageCode("ara-ayl")).isEqualTo("ar-ayl");
 
     // Special case of short codes that are actually part of a macrolanguage.
+    assertThat(Util.normalizeLanguageCode("arb")).isEqualTo("ar-arb");
     assertThat(Util.normalizeLanguageCode("nb")).isEqualTo("no-nob");
     assertThat(Util.normalizeLanguageCode("nn")).isEqualTo("no-nno");
     assertThat(Util.normalizeLanguageCode("nob")).isEqualTo("no-nob");