Move the already existing fast case for %NewObject into a dedicated
FastNewObjectStub that we can utilize in places where we would otherwise
fallback to %NewObject immediately, which is rather expensive.

Also use FastNewObjectStub as the generic implementation of JSCreate,
which should make constructor inlining based on SharedFunctionInfo (w/o
specializing to a concrete closure) viable soon.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1708313002

Cr-Commit-Position: refs/heads/master@{#34136}