Clarify that new `ConditionVariable` instances are closed

#minor-release

PiperOrigin-RevId: 546803592
(cherry picked from commit db1efe64f368173246244d8689ffc50f6ba8f5d2)

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

@@ -40,7 +40,7 @@ public class ConditionVariable {
   private final Clock clock;
   private boolean isOpen;
 
-  /** Creates an instance using {@link Clock#DEFAULT}. */
+  /** Creates a closed instance using {@link Clock#DEFAULT}. */
   public ConditionVariable() {
     this(Clock.DEFAULT);
   }