The {CompilationState} currently stores the {WasmEngine}, while the
{NativeModule} only stores the {WasmCodeManager}. From a high-level
view, this does not make much sense. The {NativeModule} belongs to
exactly one {WasmEngine}, so that link should be stored there. We can
then get to the {WasmCodeManager} from the {WasmEngine}.

This change requires a refactoring of the {WasmCodeManagerTest} which
created {WasmCodeManager}s independent of the {Isolate} and the
{WasmEngine}. This is not supported any more.
Note that in production, each {WasmEngine} owns exactly one
{WasmCodeManager} and one {WasmMemoryTracker}, so testing that a
{WasmMemoryTracker} can be shared by several {WasmCodeManager}s didn't
make sense in the first place.

R=mstarzinger@chromium.org

Bug: v8:8217
Change-Id: I582e698be35f97dbd38bf6e12eb7f8ee4fc1f0f2
Reviewed-on: https://chromium-review.googlesource.com/c/1297960
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56992}