Allow developers to specify CharSequence for Notification strings

CharSequence is used by Notification builders and allows to set Spannable text.
It's the base interface of the String class, so apps wouldn't be break after
the update.

PiperOrigin-RevId: 303731890

library/ui/src/main/java/com/google/android/exoplayer2/ui/PlayerNotificationManager.java

@@ -140,7 +140,7 @@ public class PlayerNotificationManager {
      *
      *
      * @param player The {@link Player} for which a notification is being built.
      * @param player The {@link Player} for which a notification is being built.
      */
      */
-    String getCurrentContentTitle(Player player);
+    CharSequence getCurrentContentTitle(Player player);
 
 
     /**
     /**
      * Creates a content intent for the current media item.
      * Creates a content intent for the current media item.
@@ -160,7 +160,7 @@ public class PlayerNotificationManager {
      * @param player The {@link Player} for which a notification is being built.
      * @param player The {@link Player} for which a notification is being built.
      */
      */
     @Nullable
     @Nullable
-    String getCurrentContentText(Player player);
+    CharSequence getCurrentContentText(Player player);
 
 
     /**
     /**
      * Gets the content sub text for the current media item.
      * Gets the content sub text for the current media item.
@@ -170,7 +170,7 @@ public class PlayerNotificationManager {
      * @param player The {@link Player} for which a notification is being built.
      * @param player The {@link Player} for which a notification is being built.
      */
      */
     @Nullable
     @Nullable
-    default String getCurrentSubText(Player player) {
+    default CharSequence getCurrentSubText(Player player) {
       return null;
       return null;
     }
     }