Ellise Shafer editorRobert Downey Jr. and Tom Holland have joined their “Avengers” castmates in speaking with 6-year-old Bridger Walker, who saved his younger sister from an attacking dog on July 9.Bridger’s aunt, Nicole Noel Walker, first caught the attention of Captain America actor Chris Evans with an Instagram post on July 12 in which she tagged several “Avengers” actors.