When large pages are enabled, only reserve/commit 1x seg size for LOH (#24320)

When large pages are enabled, only reserve/commit 1x seg size for LOH (#24320)

When large pages are enabled, we must commit everything we reserve.
Previously we reserved 2x the segment size for LOH. This is a problem
with large pages where we must commit everything we reserve.

Thanks to https://github.com/dotnet/coreclr/pull/24081 this does not
cause performance regression with large pages; but without large pages
we were seeing regressions when the loh_seg_size was reduced. So this
change will only take effect when large pages are enabled.