1: Clear cache entry 0 before overwriting it to maintain bookkeeping of
the SharedFunctionInfo's OSR code cache state, which tracks how many
cache entries there are for this particular SFI.

2: When inserting into the code cache, we don't know in advance whether
the entry is already present or not (this could happen with multiple
simultaneous compile jobs from different closures of the same SFI).

Fixed: chromium:1314644
Bug: v8:12161
Change-Id: I0085a3a6e0c1879c3d483853220e654aa03660ac
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3578643Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Linke <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79912}