When calling a function through a function table, check whether the
instance of the called function differs from the current instance, and
in that case call the other function via a c-wasm-entry instead of
interpreting it.
The c-wasm-entry needs to pass the wasm context, so this CL changes
this to receive the wasm context as parameter instead of embedding the
context of the calling instance.

R=titzer@chromium.org

Bug: chromium:814562, v8:7400
Change-Id: Iea93f270542169f8aac4f8c81aacec559c716368
Reviewed-on: https://chromium-review.googlesource.com/930966Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51485}