The background compile tasks should not access the NativeModule during
the main compile phase.
This CL moves on of the accessed fields into the {CompilationEnv}. It
is initialized from the existing field on the {NativeModule}.

R=titzer@chromium.org

Bug: v8:8689
Change-Id: I9738e2fb4681a035cbacf3c9e00b9e5cc9419416
Reviewed-on: https://chromium-review.googlesource.com/c/1409423Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58793}