The Isolate is only used to access the wasm engine, and the accounting
allocating. The latter is also linked directly from the wasm engine, and
the engine is linked from the native module, to which the DebugInfoImpl
already has access.
Hence, this CL removes the redundant Isolate pointers, and just accesses
the engine and the allocator via the NativeModule.

R=thibaudm@chromium.org

Change-Id: Ib51cee2d166443a34e22fa02e8ad1549328aaa7f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2214827Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67966}