Stabilize various setUserAgent() and Util.getUserAgent() methods

Issue: androidx/media#2286
PiperOrigin-RevId: 742367539

api.txt

@@ -1265,6 +1265,7 @@ package androidx.media3.common.util {
     method public static boolean checkCleartextTrafficPermitted(androidx.media3.common.MediaItem...);
     method @Nullable public static String getAdaptiveMimeTypeForContentType(@androidx.media3.common.C.ContentType int);
     method @Nullable public static java.util.UUID getDrmUuid(String);
+    method public static String getUserAgent(android.content.Context, String);
     method public static boolean handlePauseButtonAction(@Nullable androidx.media3.common.Player);
     method public static boolean handlePlayButtonAction(@Nullable androidx.media3.common.Player);
     method public static boolean handlePlayPauseButtonAction(@Nullable androidx.media3.common.Player);
@@ -1304,6 +1305,7 @@ package androidx.media3.datasource {
 
   public static final class DefaultHttpDataSource.Factory implements androidx.media3.datasource.HttpDataSource.Factory {
     ctor public DefaultHttpDataSource.Factory();
+    method public androidx.media3.datasource.DefaultHttpDataSource.Factory setUserAgent(@Nullable String);
   }
 
   public interface HttpDataSource extends androidx.media3.datasource.DataSource {
@@ -1344,6 +1346,7 @@ package androidx.media3.datasource.cronet {
 
   public static final class CronetDataSource.Factory implements androidx.media3.datasource.HttpDataSource.Factory {
     ctor public CronetDataSource.Factory(org.chromium.net.CronetEngine, java.util.concurrent.Executor);
+    method public androidx.media3.datasource.cronet.CronetDataSource.Factory setUserAgent(@Nullable String);
   }
 
   public final class CronetUtil {
@@ -1359,6 +1362,7 @@ package androidx.media3.datasource.okhttp {
 
   public static final class OkHttpDataSource.Factory implements androidx.media3.datasource.HttpDataSource.Factory {
     ctor public OkHttpDataSource.Factory(okhttp3.Call.Factory);
+    method public androidx.media3.datasource.okhttp.OkHttpDataSource.Factory setUserAgent(@Nullable String);
   }
 
 }

libraries/common/src/main/java/androidx/media3/common/util/Util.java

@@ -2075,7 +2075,6 @@ public final class Util {
    * @param applicationName String that will be prefix'ed to the generated user agent.
    * @return A user agent string generated using the applicationName and the library version.
    */
-  @UnstableApi
   public static String getUserAgent(Context context, String applicationName) {
     String versionName;
     try {

libraries/datasource/src/main/java/androidx/media3/datasource/DefaultHttpDataSource.java

@@ -103,7 +103,6 @@ public class DefaultHttpDataSource extends BaseDataSource implements HttpDataSou
      * @return This factory.
      */
     @CanIgnoreReturnValue
-    @UnstableApi
     public Factory setUserAgent(@Nullable String userAgent) {
       this.userAgent = userAgent;
       return this;

libraries/datasource/src/main/java/androidx/media3/datasource/HttpEngineDataSource.java

@@ -127,7 +127,6 @@ public final class HttpEngineDataSource extends BaseDataSource implements HttpDa
      * @return This factory.
      */
     @CanIgnoreReturnValue
-    @UnstableApi
     public Factory setUserAgent(@Nullable String userAgent) {
       this.userAgent = userAgent;
       return this;

libraries/datasource_cronet/src/main/java/androidx/media3/datasource/cronet/CronetDataSource.java

@@ -173,7 +173,6 @@ public class CronetDataSource extends BaseDataSource implements HttpDataSource {
      * @return This factory.
      */
     @CanIgnoreReturnValue
-    @UnstableApi
     public Factory setUserAgent(@Nullable String userAgent) {
       this.userAgent = userAgent;
       if (internalFallbackFactory != null) {

libraries/datasource_okhttp/src/main/java/androidx/media3/datasource/okhttp/OkHttpDataSource.java

@@ -112,7 +112,6 @@ public class OkHttpDataSource extends BaseDataSource implements HttpDataSource {
      * @return This factory.
      */
     @CanIgnoreReturnValue
-    @UnstableApi
     public Factory setUserAgent(@Nullable String userAgent) {
       this.userAgent = userAgent;
       return this;

libraries/transformer/src/androidTest/java/androidx/media3/transformer/TransformerGapsTest.java

@@ -38,10 +38,10 @@ import org.junit.runner.RunWith;
 
 /**
  * End-to-end instrumentation tests for {@link Transformer} when the {@link EditedMediaItemSequence}
- * has video gaps.
+ * has gaps.
  */
 @RunWith(AndroidJUnit4.class)
-public class TransformerVideoGapsTest {
+public class TransformerGapsTest {
   private static final EditedMediaItem AUDIO_VIDEO_MEDIA_ITEM =
       new EditedMediaItem.Builder(MediaItem.fromUri(MP4_ASSET.uri)).build();
   private static final EditedMediaItem AUDIO_ONLY_MEDIA_ITEM =