This patch implements the access of private accessors by loading the
referenced component from the AccessorPair associated with private
name variables. It also makes the error messages for invalid kind
of private accessor access more specific.

Bug: v8:8330
Design doc: https://docs.google.com/document/d/10W4begYfs7lmldSqBoQBBt_BKamgT8igqxF9u50RGrI/edit

Change-Id: I6d441cffb85f8d9cd0417ec9b6ae20f3e34ef418
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1695205Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Cr-Commit-Position: refs/heads/master@{#63474}