message: Mark the InternalKeyManager as alpha.
  It should be public (once it's done everyone can use it), but currently it's alpha.
  GitOrigin-RevId:
diff: package com.google.crypto.tink;
  +import com.google.crypto.tink.annotations.Alpha;
  import com.google.crypto.tink.proto.KeyData.KeyMaterialType;
  import com.google.protobuf.ByteString;
  import com.google.protobuf.InvalidProtocolBufferException;
  @@ -47,6 +48,7 @@ import java.util.Set;
  * #keyFactory}. In this case it needs to return an object of type {@code KeyFactory<KeyFormatProto,
  * KeyProtoT>}, where one has to specify a proto for the key format as well.
  */
  +@Alpha
  public abstract class InternalKeyManager<KeyProtoT extends MessageLite> {
  /** A PrimitiveFactory knows how to create primitives from a given key. */
  protected abstract static class PrimitiveFactory<PrimitiveT, KeyT> {
  