This CL moves all heap-allocated WASM data structures, both ones
that are bonafide JSObjects and ones that are FixedArrays only, into a
consistent place with consistent layout. Note that not all accessors are complete, and I haven't fully spread the new static typing goodness
to all places in the code.

R=ahaas@chromium.org,rossberg@chromium.org
CC=gdeepti@chromium.org,mtrofin@chromium.org,clemensh@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2490663002
Cr-Commit-Position: refs/heads/master@{#40913}