I'm mainly familiar with this exercise with the other arm reaching up to reach the arm going down. My fitness program with GMB calls it "Shoulder Combined Motions". When I was a child, checking out yoga books, they called it the "Cow pose", but that's typically used to refer to a different pose, and instead you'll see it called "Cow Face pose", or Gomukhasana (and technically also involves a particular leg positioning).
When we did it in martial arts or soccer warmups more like what you show in the image, it was simply described as "reach your arm over your head and down your back, and lightly push down on the elbow with your other hand while resisting with the stretching arm."