* Kernel/Process: Notify the CPUs that a new pagetable has been set every time the process they're executing changes.
Previously the page table would only be changed when the current CPU's page table was changed, this lead to stale JIT states and the PC going to 0 when context-switching a different core inside the ThreadManager::SwitchContext function because the JIT for a new pagetable is only constructed upon receiving the change notification.
* Kernel/Process: Use the relevant CPU's last process to determine when to switch its current process.
Previously it was checking the kernel's current_process variable, which gets overwritten every time a CPU runs its slice. The rescheduling happens after all CPUs have run their slice so the code was effectively only checking the last CPU's process.
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