‘Small Axe: Alex Wheatle’ Film Review: Steve McQueen Captures the Process of an Artist Discovering Himself

“You can’t look forward without looking back.” That’s a valuable piece of advice given to the protagonist of “Alex Wheatle,” but it’s also a summation of what director and co-writer Steve McQueen is doing with his extraordinary “Small Axe” series. (“Alex Wheatle,” the fourth of five titles, premieres on Amazon Dec. 11.) With its vivid…