benchmark: avoid TurboFan deopt in arrays bench

Something unidentified at the moment is causing the arrays benchmarks to
deopt when run with the TurboFan compiler. Refactor the test to use an
inner function that can be correctly optimized by TurboFan and
Crankshaft.

PR-URL: https://github.com/nodejs/node/pull/11894
Ref: https://github.com/nodejs/node/issues/11851#issuecomment-287106714


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>