Common: Add constexpr Fill function

Source/Core/Common/TypeUtils.h

@@ -83,4 +83,17 @@ static_assert(!IsNOf<int, 1, int, int>::value);
 static_assert(IsNOf<int, 2, int, int>::value);
 static_assert(IsNOf<int, 2, int, short>::value);  // Type conversions ARE allowed
 static_assert(!IsNOf<int, 2, int, char*>::value);
+
+// TODO: This can be replaced with std::array's fill() once C++20 is fully supported.
+// Prior to C++20, std::array's fill() function is, unfortunately, not constexpr.
+// Ditto for <algorithm>'s std::fill. Although Dolphin targets C++20, Android doesn't
+// seem to properly support constexpr fill(), so we need this for now.
+template <typename T1, size_t N, typename T2>
+constexpr void Fill(std::array<T1, N>& array, const T2& value)
+{
+  for (auto& entry : array)
+  {
+    entry = value;
+  }
+}
 }  // namespace Common