“Wonka,” a sugary prequel to Roald Dahl’s “Charlie and the Chocolate Factory,” delivers not so much a world of pure imagination as a land of constant cuteness. Of course it does. The affable musical film, starring Timothée Chalamet, is directed by Paul King, the King of “Aww”s, who made heart-warming hits out of “Paddington” and “Paddington 2.”