Common: Add alignment header

Gets rid of duplicated alignment code.

Source/Core/Common/Align.h

@@ -0,0 +1,24 @@
+// This file is under the public domain.
+
+#pragma once
+
+#include <cstddef>
+#include <type_traits>
+
+namespace Common
+{
+template <typename T>
+constexpr T AlignUp(T value, size_t size)
+{
+  static_assert(std::is_unsigned<T>(), "T must be an unsigned value.");
+  return static_cast<T>(value + (size - value % size) % size);
+}
+
+template <typename T>
+constexpr T AlignDown(T value, size_t size)
+{
+  static_assert(std::is_unsigned<T>(), "T must be an unsigned value.");
+  return static_cast<T>(value - value % size);
+}
+
+}  // namespace Common