Introduce a generic register context for SVCs

`SvcContext` represents a common interface for accessing registers from SVCs, decoupling them from a particular thread context.

app/src/main/cpp/skyline/common/wregister.h

@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Copyright © 2023 Strato Team and Contributors (https://github.com/strato-emu/)
+
+#pragma once
+
+#include <common/base.h>
+
+namespace skyline {
+    struct WRegister {
+        u32 lower;
+        u32 upper;
+
+        constexpr operator u32() const {
+            return lower;
+        }
+
+        void operator=(u32 value) {
+            lower = value;
+            upper = 0;
+        }
+    };
+}