Use macros to unify how HashTable (and subclasses) are marked as
externally specialised, and how those specialisations are initialised.

This cleanup will make it easier in the future to also add
specialisations of HashTable methods for Isolate/OffThreadIsolate.

Bug: chromium:1011762
Change-Id: Ibb62cf30d3ba40170e1d35ab72ada0f74963a5c4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2083023
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66528}