protobuf-lite: ProtoLiteUtils experimental comment (#10627)

Add a comment clarifying that the ProtoLiteUtils class will remain
experimental.

Author: temawi

protobuf-lite/src/main/java/io/grpc/protobuf/lite/ProtoLiteUtils.java

@@ -38,8 +38,12 @@
 
 /**
  * Utility methods for using protobuf with grpc.
+ *
+ * <p>Note that this class will remain experimental for the foreseeable future as the proto lite
+ * API, which this class depends on, is not guaranteed to be stable. This is explained in protobuf
+ * documentation at: https://github.com/protocolbuffers/protobuf/blob/main/java/lite.md
  */
-@ExperimentalApi("Experimental until Lite is stable in protobuf")
+@ExperimentalApi("Will remain experimental as protobuf lite API is not stable")
 public final class ProtoLiteUtils {
 
   // default visibility to avoid synthetic accessors