The NCI cache depends on the script cache (which is essentially a
SharedFunctionInfo cache, and the SFIs contain bytecode) to
deduplicate SFIs across native contexts. NCI caching does not work
without script caching. Thus the lifetimes of both caches should
match; in particular, disabling cache ageing for NCI is only effective
if script cache ageing is also disabled.

This CL adds an --isolate-script-cache-ageing flag. It's separate from
the --turbo-nci-cache-ageing flag s.t. we can disable script cache
ageing *without NCI* for benchmarking purposes.

Future work: Good ageing heuristics for both script and nci caches.

Bug: v8:8888
Change-Id: Ia5546feeced5821a538d97db1bb8f5bb92528114
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2452471
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70339}