Adds a instance types for each HashTable subtype, rather than reusing
HASH_TABLE_TYPE. This allows us to check for these types by checking
the instance type directly, rather than by comparing against the map in
the root set.

Also, as a drive-by, do the same for SCRIPT_CONTEXT_TABLE_TYPE, and use
instance type checks rather than map checks for Context types.

This is a good general clean-up, but in particular is intended for
GetIsolate removal.

TBR=jarin@chromium.org

Bug: v8:7786
Change-Id: I420abdd12906dfa20c922e486ecdc657eb3c6ef0
Reviewed-on: https://chromium-review.googlesource.com/1114958Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54128}