kernel/process: Make the handle table per-process

In the kernel, there isn't a singular handle table that everything gets
tossed into or used, rather, each process gets its own handle table that
it uses. This currently isn't an issue for us, since we only execute one
process at the moment, but we may as well get this out of the way so
it's not a headache later on.

src/core/hle/kernel/thread.cpp

@@ -266,7 +266,7 @@ SharedPtr<Thread> SetupMainThread(KernelCore& kernel, VAddr entry_point, u32 pri
     SharedPtr<Thread> thread = std::move(thread_res).Unwrap();
 
     // Register 1 must be a handle to the main thread
-    const Handle guest_handle = kernel.HandleTable().Create(thread).Unwrap();
+    const Handle guest_handle = owner_process.GetHandleTable().Create(thread).Unwrap();
     thread->SetGuestHandle(guest_handle);
     thread->GetContext().cpu_registers[1] = guest_handle;