In preparation for converting these stubs to builtins. This turns the
compile-time IsJSArray parameter into a runtime check.

Bug: v8:7777
Change-Id: Ief44e7cd77e772809e50618e55f51268e9ac8ad9
Reviewed-on: https://chromium-review.googlesource.com/c/1339868
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57594}