core/hle/kernel: Split transfer memory handling out into its own class

Within the kernel, shared memory and transfer memory facilities exist as
completely different kernel objects. They also have different validity
checking as well. Therefore, we shouldn't be treating the two as the
same kind of memory.

They also differ in terms of their behavioral aspect as well. Shared
memory is intended for sharing memory between processes, while transfer
memory is intended to be for transferring memory to other processes.

This breaks out the handling for transfer memory into its own class and
treats it as its own kernel object. This is also important when we
consider resource limits as well. Particularly because transfer memory
is limited by the resource limit value set for it.

While we currently don't handle resource limit testing against objects
yet (but we do allow setting them), this will make implementing that
behavior much easier in the future, as we don't need to distinguish
between shared memory and transfer memory allocations in the same place.