With this CL, FeedbackCells now own an entry in the JSDispatchTable.
The entry is not yet populated, but it is already managed by the GC. In
follow-up CLs, the entry handle will be populated to point to the
current code for the functions sharing the FeedbackCell.

Bug: 40931165, 42204201
Change-Id: I4f2cb6850b31ba7fc7af7460a3f8e9d5a0b9ed65
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/5677828


Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Olivier Flückiger <olivf@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#95130}