message: Simplify initialization of test FrameGeneratorCapturerConfig.
  Allowing assignment of the AutoOpt fields:
  AutoOpt<T> field = T();
  Cr-Commit-Position: refs/heads/master@{#30674}
diff: @@ -29,6 +29,7 @@ namespace frame_gen_cap_impl {
  template <typename T>
  class AutoOpt : public absl::optional<T> {
  public:
  + using absl::optional<T>::optional;
  T* operator->() {
  if (!absl::optional<T>::has_value())
  this->emplace(T());
  