This is a reland of bf2f0a02

Original change's description:
> [builtins] Support embedded builtins in nosnapshot builds
>
> This CL adds support for embedded builtins in nosnap builds by creating
> and setting an 'embedded blob' after builtin generation. Unlike
> snapshot builds, the blob is not embedded into the .text section but
> located on the C++ heap.
>
> This makes nosnap builds more consistent with mksnapshot, and allows us
> to simplify there and in serializer cctests.
>
> Complications arise from the different workflows we need to support:
>
> 1. the standard mksnapshot build process,
> 2. nosnap builds (which reuse the blob created by the first Isolate),
> 2. and tests with various complicated serialization workflows.
>
> To cover all of these cases, this CL introduces two knobs to twiddle:
>
> 1. A 'sticky' embedded blob which overrides compiled-in default
>    embedded blobs at Isolate setup.
> 2. The blob lifecycle can be managed manually or through refcounting.
>
> These are described in more detail in isolate.cc.
>
> Tbr: ulan@chromium.org
> Bug: v8:6666, v8:8350
> Change-Id: I3842e40cdaf45d2cadd05c6eb1ec2f5e3d83568d
> Reviewed-on: https://chromium-review.googlesource.com/c/1310195
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#57523}

Tbr: ulan@chromium.org,yangguo@chromium.org
Bug: v8:6666, v8:8350
Change-Id: I13b523c9e7406b39a3cd28465c06f17f1744a738
Reviewed-on: https://chromium-review.googlesource.com/c/1337578
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57540}