* Replace deprecated Factory::NewFunction* calls with JSFunctionBuilder.
* Drive-by: rename Factory::NewFunctionForTest to ..ForTesting (this is
  the correct suffix recognized by our tooling to ensure it's only
  called from tests).

Tbr: clemensb@chromium.org
Bug: v8:8888
Change-Id: I110063803e5b467bd91b75fe8fea2ca4174f2bcc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2529129Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71101}