This change
- adds new maps for elements, global, and named dictionaries.
- adds support to embed these dictionaries in the startup snapshot.
- adds support to embed these dictionaries in the code cache.
- refactors the rehashing logic.

R=ishell@chromium.org, jgruber@chromium.org, mstarzinger@chromium.org

Bug: v8:6593
Change-Id: I8d9a7ba7145f1af4e6e15301a4d5611f07c77f33
Reviewed-on: https://chromium-review.googlesource.com/753323Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49155}