We pass the {WasmModule} by non-const pointer and by non-const
reference a lot. This violates the style guide, and adds the risk of
accidentally modifying it.
This CL makes the {WasmModule} const during compilation and
instantiation.

R=mstarzinger@chromium.org

Bug: v8:7754
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Ie1878322828b63284b341d97da595e8e91dd4f51
Reviewed-on: https://chromium-review.googlesource.com/1117194Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54078}