vm: implement B_RANDOMIZED_IMAGE_ADDRESS address specification

On some 64 bit architectures program and library images have to be mapped in
the lower 2 GB of the address space (due to instruction pointer relative
addressing). Address specification B_RANDOMIZED_IMAGE_ADDRESS ensures that
created area satisfies that requirement.
runtime_loader: use long type for region delta
x86_64: put user stack and team data at top of user address space
vm: several improvements to VMUserAddressSpace::_InsertAreaSlot implementation
 * B_BASE_ADDRESS honors requested alignment
 * end of range is honored
 * B_BASE_ADDRESS reuses B_ANY_ADDRESS code