This patch implements the MegaDOM IC setup and access. A new MegaDOM
IC state indicates that we've seen only DOM accessors at this access
site.

This CL only adds support for DOM getters in LoadIC, other kinds of
access will be added in follow on CLs.

Still remaining TODO before shipping:
1. Have a mechanism to invalidate the protector
2. Have a mechanism to find the accessors that aren't overloaded
3. Use a new builtin to miss to runtime on access check failure

Change-Id: Ie12efe5e9fa284f023043b996d61e7d74e710ee2
Bug: v8:11321
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2618239Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73733}