This CL adds static assertions (in Liftoff) and DCHECKs (in wasm
compiler) to validate that the size of loaded fields from the wasm
instance object matches the expected size. This is to avoid future bugs
where we change the size of integer fields and forget to update all
code that uses these fields.

R=titzer@chromium.org

Bug: v8:8130, v8:6600
Change-Id: Ib7273800029135b851c0f0b1ca52886783b61fb0
Reviewed-on: https://chromium-review.googlesource.com/1203836
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55651}