os::attempt_reserve_at:

We currently use `log_info(os)` in os::attempt_reserve_memory_at. Those logs are useful, but arguably too unfocused. It makes sense to specialize them more (e.g. os+map or similar), and tone down at least the reservation errors to trace level.

os::reserve_memory:
os::reserve_memory_special:

We don't log at all.

Additionally, check against logging in ReservedSpace. If logging at the os level is consistent and covers all needed cases, we may be able to remove logging from ReservedSpace altogether.