CompilationSubCache has some complexity regarding generations of tables
which is only used by one subclass, CompilationCacheRegExp. This change
adjusts the class hierarchy so that classes only contain the necessary
member functions.

Bug: v8:12808
Change-Id: I4f4cf15bbf9b80c2de0c18aea82a0c238804759d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3629603Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#80506}