For implementing wasm GC we need to revisit all places where we hold
WasmCode*. This CL reduces these places.

R=mstarzinger@chromium.org

Bug: v8:8217
Change-Id: I869e3c1817a3b9a24ab6aa281c0688bdf890dd33
Reviewed-on: https://chromium-review.googlesource.com/c/1297951Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56942}