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.

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

Bug: v8:6593
Change-Id: I2455fe2a9cc6e93247940de99de5f124c2ada137
Reviewed-on: https://chromium-review.googlesource.com/756693Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49167}