Reland "[debugger] Rewrite the ScopeIterator/DebugEvaluate to use Scope rather than ScopeInfo for inner scopes."

Change-Id: I0ad97057600d0a0f1dd4c71d5f8245dafb908154
Reviewed-on: https://chromium-review.googlesource.com/1103576Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53781}