Revert of [key-accumulator] Starting to reimplement the key-accumulator (patchset #14 id:260001 of https://codereview.chromium.org/1707743002/ )

Reason for revert:
gcmole failure https://build.chromium.org/p/client.v8/builders/V8%20Linux/builds/8598

Original issue's description:
> [key-accumulator] Starting to reimplement the key-accumulator
>
> Introducing the KeyAccumulator accidentally removed some crucial fast-paths.
> This CL starts rewriting the KeyAccumulator, step-by-step introducing the
> special cases again.
>
> BUG=chromium:545503, v8:4758
> LOG=y
>
> Committed: https://crrev.com/9c61327ecb2ee41f34232632e0cac93202bae6b7
> Cr-Commit-Position: refs/heads/master@{#34532}

TBR=verwaest@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:545503, v8:4758

Review URL: https://codereview.chromium.org/1773593003

Cr-Commit-Position: refs/heads/master@{#34537}