This removes the redundant weak link to the {WasmCompiledModule} from
the {CompilationState} class and instead replaces it with a normal C++
pointer back to the associated {NativeModule}. This reduces the number
of weak links back into the garbage collected heap, such links are
costly for the GC, hard to understand and maintain, and should be kept
at a minimum. Simply explicitly encoding the one-to-one relationship
between the {NativeModule} and the {CompilationState} is easier.

R=clemensh@chromium.org

Change-Id: Ib7f79bc3a89fe463f548615a918f3fa4c9feea59
Reviewed-on: https://chromium-review.googlesource.com/995274Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52348}