“Loving Vincent” is, indisputably, a technical achievement. Each one of the ambitious animated film’s 65,000 frames is an oil painting, created by a classically trained artist in the style — or, rather, in the various styles — of painter Vincent Van Gogh. More than 100 painters worked together to create the film, which follows an acquaintance of the artist who is trying to uncover how and why Van Gogh died in 1890, at 37. Visually, it’s spectacular.