I need to take an integer value and convert it so that when it is represented in hexadecimal, the digits are reversed. For instance:

```
Dim a As Integer = &H4321
Dim a_changedorder As Integer = ReverseHexDigits(a)
Console.Writeline(a_changedorder.ToString("X4")) ' Should output 1234

```

How can I implement a `ReverseHexDigits` method that works like that?

As a second example, `&H4F2A` should become `&HA2F4`.