Issue with `.trace` on a `.val()` expression fixed with `.val_op()`

Description

Here's the code:

TEST(Whatever, whatever3) {
  using stan::math::var;
  Eigen::Matrix<var, -1, 1> a(3);
  Eigen::VectorXd b(3);

  a << 1, 1, 1;

  b << 0.001, 0.01, 0.1;

  std::cout << "val no trace: " << a.val().transpose() * b << std::endl;
  std::cout << "val trace: " << (a.val().transpose() * b).trace() << std::endl;
  std::cout << "val_op no trace: " << a.val_op().transpose() * b << std::endl;
  std::cout << "val_op trace: " << (a.val_op().transpose() * b).trace() << std::endl;
}

Output is:

val no trace: 0.111
val trace: 0.001
val_op no trace: 0.111
val_op trace: 0.111

The correct output is 0.111.

So it looks like with .trace() and .val() only the first element of the expression is being evaluated but .val_op() makes it all the way through.

Current Version:

v3.4.0

Start by reproducing the provided C++ example and comparing the .val() and .val_op() paths for the Eigen expression involving .trace(). Done means the trace expression produces the full expected value, 0.111, rather than only the first element.