As a first step towards freeing CodeEntry objects that are neither still
referenced by JS or stored in a profile, enable freeing of refcounted
strings by CodeEntry instances. For now, this leaves behaviour unchanged
until we receive CodeEntry destruction events.

Bug: v8:11054
Change-Id: Iabd05aa730343cd1a879ff5b04326f23e68aa948
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2590604
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71858}