Migrates all of the direct mapping facilities over to the new memory
class. In the process, this also obsoletes the need for memory_setup.h,
so we can remove it entirely from the project.

This allows kernel internal type processes to be assigned IDs in the KIP range while userland processes are assigned in the user range.

Centralizes the page table switching to one spot, rather than making
calling code deal with it everywhere.

Now that we have the address arbiter extracted to its own class, we can
fix an innaccuracy with the kernel. Said inaccuracy being that there
isn't only one address arbiter. Each process instance contains its own
AddressArbiter instance in the actual kernel.

This fixes that and gets rid of another long-standing issue that could
arise when attempting to create more than one process.

Allows getting rid of reliance on the global accessor functions and
instead operating on the provided system instance.

* get rid of boost::optional

* Remove optional references

* Use std::reference_wrapper for optional references

* Fix clang format

* Fix clang format part 2

* Adressed feedback

* Fix clang format and MacOS build

There's no real need to use a shared pointer in these cases, and only
makes object management more fragile in terms of how easy it would be to
introduce cycles. Instead, just do the simple thing of using a regular
pointer. Much of this is just a hold-over from citra anyways.

It also doesn't make sense from a behavioral point of view for a
process' thread to prolong the lifetime of the process itself (the
process is supposed to own the thread, not the other way around).