This makes several changes to SwitchStatement handling:

  - Store the CaseClause list inline (as it's always allocated)
  - Only rewrite with additional blocks if the Block Scope for
    the switch statement isn't empty
  - Use Parser::IgnoreCompletion() instead of inserting an additional
    `undefined` ExpressionStatement

Bug: v8:6092
Change-Id: Ib08d0ba851dd8e78b3dc74782b8e554541e79182
Reviewed-on: https://chromium-review.googlesource.com/644176Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47751}