On windows, when changing permissions for a range of pages, or
committing or discarding a range of pages, we need to split that range
by the reservations and potentially execute several system calls. This
logic is currently implemented for committing memory.
This CL extracts this to a helper function such that we can reuse this
for discarding a range of pages.

R=mstarzinger@chromium.org

Bug: v8:8217
Change-Id: I65673eebe28362975f0165905d20b97ef7947f56
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1611544
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61523}