The %GetPrototype runtime function does a lot more than the
GetSuperConstructor specified in ES6 12.3.5.2. So this introduces a
proper %_GetSuperConstructor instead with support in TurboFan.

R=jarin@chromium.org, rossberg@chromium.org

Review URL: https://codereview.chromium.org/1522503002

Cr-Commit-Position: refs/heads/master@{#32804}