Interpreter entries may be called from wasm functions, when debugging.
That means that, when moving on the native heap, interpreter entries
need to be native, too. That means they cannot reference movable GC
objects.

The only such reference was to the instance object, which is needed
in the WasmRunInterpreter runtime function. We can fetch the instance
using GetWasmInstanceOnTop() instead.

Bug: v8:6876
Change-Id: I7198a849cc0e441b057537a570a3dfa6f3197149
Reviewed-on: https://chromium-review.googlesource.com/742391
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49019}