[builtins] Removing %_CallFunction in GetThirdIndex.
[builtins] Removing %_CallFunction in GetThirdIndex.

By using an InternArray for the pivot calculation we can get rid of yet
another %_CallFunction.

Review URL: https://codereview.chromium.org/1316673008

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#30636}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh