To enable deallocation of CodeEntry objects after they're no longer
being referenced by an active profile or alive on the heap, replace the
|used| bit with a proper reference count maintained by a CodeMap.

Bug: v8:11054
Change-Id: I3016cdbcbd1b4e8a26c3b1689e968cb2eef8e6d8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2965493Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#75193}