Introduce DEFINE_FIELD_OFFSET_CONSTANTS macro for defining a contiguous
sequence of field offsets.
In addition, this CL turns last two Smi fields to int fields.

Bug: v8:6470
Change-Id: I12a6ad8d7b444772dbc01bba6734080f1d5eccdc
Reviewed-on: https://chromium-review.googlesource.com/532913Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45917}