This is a reland of f1b1ec70

Original change's description:
> [builtins] Remove off-heap builtins from the snapshot
>
> This CL is the final major step towards shipping off-heap-safe builtins
> embedded into the binary.
>
> Prior to snapshot serialization, we now:
> * create the embedded blob containing off-heap instruction streams,
> * use that to generate embedded.cc (containing embedded binary data),
> * replace off-heap-safe builtins with trampolines,
> * and serialize those into the final snapshot.
>
> The new RelocInfo::OFF_HEAP_TARGET kind is used to fix up trampoline
> targets on deserialization.
>
> Bug: v8:6666
> Change-Id: Ib07aea9e3bd7ecdec42291c1388b3a7453ea96ce
> Reviewed-on: https://chromium-review.googlesource.com/950775
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51960}

TBR=yangguo@chromium.org,mstarzinger@chromium.org

Cq-Include-Trybots: luci.v8.try:v8_mac64_dbg,v8_mac64_rel
Bug: v8:6666
Change-Id: Id9954af3c8195754ff3658c4603858904fcf88c4
Reviewed-on: https://chromium-review.googlesource.com/964481
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52006}