The memory.init and memory.drop instructions have a data segment index
that can only be validated by knowing the number of data segments. This
information is provided by the new DataCount section.

Bug: v8:7747
Change-Id: Ie04d57584fe028637f6e931ab53d00abc5b998a4
Reviewed-on: https://chromium-review.googlesource.com/c/1355624Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58031}