... containing RootsTable, ExternalReferenceTable, builtins array and
potentially some other data that can be accessed via the RootRegister.

This is a preliminary step before adding support for pointer-compression
friendly heap layout.

Bug: v8:8182
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I2899f657aaff1351a5304afa0b1a4c5ae4cfc31d
Reviewed-on: https://chromium-review.googlesource.com/c/1245426Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56551}