Since TurboAssembler::CallBuiltinPointer actually takes the
builtin_index as input, rename the function to CallBuiltinByIndex.

Bug: v8:9183
Change-Id: I4958d96f18a48a2ec91525d80d597a35e45d5989
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1657915
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62151}