It is better to infer the language mode from the context and the closure
instead of getting it from the feedback vector. This will allow us to use
some of these builtins even when feedback vectors are not allocated.
Language mode is only needed to decide if we need to throw an exception
when a store fails. This is on a slow path and hence deriving the language
mode is not on critical path.

Bug: v8:8580
Change-Id: Id0d8e78d35046f015b5cdc15d5fc3f8a17dd8757
Reviewed-on: https://chromium-review.googlesource.com/c/1421924
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59113}