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: Id3d5941e509504415692f833e406ecdd2553d426
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2945541Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#75164}