This is a reland of fa18e78d.

Mips compile error is fixed.

Original change's description:
> [wasm] [cleanup] Only pass information really needed
>
> Instead of always passing the MachineType, we can often just pass the
> accessed memory size or the MachineRepresentation, which is less
> information to pass and will simplify the upcoming refactoring for
> memory operations in Liftoff.
>
> R=titzer@chromium.org
>
> Bug: v8:6600
> Change-Id: I8748f8e00dcfdbc4082893143fe88bdafde99053
> Reviewed-on: https://chromium-review.googlesource.com/822194
> Reviewed-by: Ben Titzer <titzer@chromium.org>
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50041}

TBR=titzer@chromium.org

Bug: v8:6600
Change-Id: I3dff3072d6ceebd74873ace0c7dce7cccc3055d5
Reviewed-on: https://chromium-review.googlesource.com/822851Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50050}