This reverts commit 2f2ce7b7.

Reason for revert:
https://bugs.chromium.org/p/chromium/issues/detail?id=865494

Original change's description:
> [turbofan] Remove optimization for NumberToString
>
> We used to have an optimized version for ToString on number nodes
> which was allocating an object on the heap, therefore
> preventing this code from being executed on the compiler thread.
> Octane benchmark results show insignificant increase in performance
> (< 0.5%) without this optimization - see
> https://docs.google.com/spreadsheets/d/1MC5NrMoMSsqxZqw0ojoZvomBb7q2EOt1S0sFoJ8ld2c/edit#gid=1732639373
> which leads to the conclusion we can safely remove the optimization for now.
>
> Bug: v8:7790
> Change-Id: Ia1d53608f8d10ba20e0ff57cccb34583655382c6
> Reviewed-on: https://chromium-review.googlesource.com/1139063
> Commit-Queue: Maya Lekova <mslekova@chromium.org>
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Reviewed-by: Georg Neis <neis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#54495}

TBR=jarin@chromium.org,neis@chromium.org,mslekova@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:7790, chromium:865494
Change-Id: I4b6c620e88c84ae889ce403fa46672db0d3b17c3
Reviewed-on: https://chromium-review.googlesource.com/1166783
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54959}