This is a reland of
https://chromium-review.googlesource.com/c/v8/v8/+/1276468, without the
change "Also forces all non-trampoline RelocInfo ByteArrays for builtins
to be generated into RO_SPACE."

Creates a single RelocInfo to be used by all builtin trampolines and
stores it as a root. All trampolines then substitute this for their
trampoline at generation time with DCHECKs to make sure it is
identical.

On x64, this results in the OLD_SPACE part of the startup snapshot
decreasing in size from 165656 to 130808 (-34848) bytes and RO_SPACE
(in the read-only snapshot) increasing from 31248 to 31272 (+24) bytes.

Bug: v8:8295
Change-Id: I0dee7dfaccd9b8025d7707b0bb90194173f1ee89
Reviewed-on: https://chromium-review.googlesource.com/c/1296459
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56930}