Add @RequiresApi(18) for FrameworkMediaDrm

Without this Android Studio shows a warning for newInstance.

PiperOrigin-RevId: 272660373

library/core/src/main/java/com/google/android/exoplayer2/drm/FrameworkMediaDrm.java

@@ -25,6 +25,7 @@ import android.media.NotProvisionedException;
 import android.media.UnsupportedSchemeException;
 import android.text.TextUtils;
 import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.drm.DrmInitData.SchemeData;
 import com.google.android.exoplayer2.extractor.mp4.PsshAtomUtil;
@@ -42,10 +43,9 @@ import java.util.List;
 import java.util.Map;
 import java.util.UUID;
 
-/**
- * An {@link ExoMediaDrm} implementation that wraps the framework {@link MediaDrm}.
- */
+/** An {@link ExoMediaDrm} implementation that wraps the framework {@link MediaDrm}. */
 @TargetApi(23)
+@RequiresApi(18)
 public final class FrameworkMediaDrm implements ExoMediaDrm<FrameworkMediaCrypto> {
 
   private static final String TAG = "FrameworkMediaDrm";