Add missing imports in `Metadata`

PiperOrigin-RevId: 459533055
(cherry picked from commit 320dcadf)

library/common/src/main/java/com/google/android/exoplayer2/metadata/Metadata.java

@@ -18,8 +18,10 @@ package com.google.android.exoplayer2.metadata;
 import android.os.Parcel;
 import android.os.Parcel;
 import android.os.Parcelable;
 import android.os.Parcelable;
 import androidx.annotation.Nullable;
 import androidx.annotation.Nullable;
+import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.MediaMetadata;
 import com.google.android.exoplayer2.MediaMetadata;
+import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.util.Util;
 import com.google.android.exoplayer2.util.Util;
 import com.google.common.primitives.Longs;
 import com.google.common.primitives.Longs;
 import java.util.Arrays;
 import java.util.Arrays;