message: flexbuffers: Add variant of Blob() that takes a key
diff: @@ -1072,6 +1072,15 @@ class Builder FLATBUFFERS_FINAL_CLASS {
  return CreateBlob(flatbuffers::vector_data(v), v.size(), 0, FBT_BLOB);
  }
  + void Blob(const char *key, const void *data, size_t len) {
  + Key(key);
  + Blob(data, len);
  + }
  + void Blob(const char *key, const std::vector<uint8_t> &v) {
  + Key(key);
  + Blob(v);
  + }
  +
  // TODO(wvo): support all the FlexBuffer types (like flexbuffers::String),
  // e.g. Vector etc. Also in overloaded versions.
  // Also some FlatBuffers types?
  