Reduce inclusion of limits.h as much as possible at the same time.
This does mean that kmalloc.h is now including Kernel/API/POSIX/limits.h
instead of LibC/limits.h, but the scope could be limited a lot more.
Basically every file in the kernel includes kmalloc.h, and needs the
limits.h include for PAGE_SIZE.
This patch stops using VirtualRangeAllocator in AddressSpace and instead
looks for holes in the region tree when allocating VM space.
There are many benefits:
- VirtualRangeAllocator is non-intrusive and would call kmalloc/kfree
when used. This new solution is allocation-free. This was a source
of unpleasant MM/kmalloc deadlocks.
- We consolidate authority on what the address space looks like in a
single place. Previously, we had both the range allocator *and* the
region tree both being used to determine if an address was valid.
Now there is only the region tree.
- Deallocation of VM when splitting regions is no longer complicated,
as we don't need to keep two separate trees in sync.
We now use AK::Error and AK::ErrorOr<T> in both kernel and userspace!
This was a slightly tedious refactoring that took a long time, so it's
not unlikely that some bugs crept in.
Nevertheless, it does pass basic functionality testing, and it's just
real nice to finally see the same pattern in all contexts. :^)
...and also RangeAllocator => VirtualRangeAllocator.
This clarifies that the ranges we're dealing with are *virtual* memory
ranges and not anything else.
