This introduces a ToNumeric conversion to the runtime and interpreter.
ToNumeric behaves like ToNumber, except that it also lets BigInts pass.

Bug: v8:6791
Change-Id: Idf9d0b5d283638459fe5893de41cc120356247a7
Reviewed-on: https://chromium-review.googlesource.com/707013
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48440}