- Fixes some incorrect assumptions about padding in the
  code generation. Slots may have apparent extra padding
  when allocation fragments go unused.
- Reworks 32 bit push code to simplify skipping slot gaps
  when 'push' instructions are used.
- Adds a ElementSizeInPointers function on machine
  representations.

Bug: chromium:1171759,v8:9198

Change-Id: I029e300fa9c306d7e35344576fd1c68857cf2bca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2660379
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72502}