- Add a new ClassScope for block scopes created for classes.
- Add a VariableMap in the class scope for private name resolution,
  and a separate UnresolvedList for private names that will be resolved
  only using ClassScopes. These are stored in RareData and will only be
  allocated when there are private name declaration or access in the
  class.

Design: https://docs.google.com/document/d/1l-D70uaHzXU8QVgQZ3ACikb3FLO6LTAfQVdGDXsh5mw/edit?usp=sharing

TBR: hpayer@chromium.org
Bug: v8:8330
Bug: v8:7468
Change-Id: I78191fc075f7f195f6c56c959773c382346cce8a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1488271
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60726}