This is a reland of 5bbd1921

Original change's description:
> [scanner] Inlining ScanIdentifier and Token check
>
> This improves parse time for code-load and other benchmarks.
>
> Bug: v8:7926
> Change-Id: I9c8017f2e7f73dd952c025db5abe8e4062e6ef9b
> Reviewed-on: https://chromium-review.googlesource.com/1196506
> Commit-Queue: Florian Sattler <sattlerf@google.com>
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55521}

TBR=verwaest@chromium.org,marja@chromium.org

Bug: v8:7926
Change-Id: I35f265a2a2189325daaf4a361bda35bf82758b16
Reviewed-on: https://chromium-review.googlesource.com/1203731Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55612}