This makes it easier to publish them in batches. Function index and
requested compilation tier are duplicated from the WasmCompilationUnit.

R=titzer@chromium.org

Bug: v8:8916
Change-Id: I87852670be029b1d729f98f01729362ca379fb50
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1529009Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60325}