Replace several NewStringFromStaticChars calls with the explicit root
string access.

Bug: v8:9396
Change-Id: I381e676fa81de24e892afe703b804b7c724a6083
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1774719Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63429}