fix: Set focus to first field in macro popup

[warmans]

Resolves: #2473

I've not touched Java in many years so this solution is taken mostly from here:

https://tips4java.wordpress.com/2010/03/14/dialog-focus/

It seems to behave differently on different platforms. HierarchyListener was the only listener that worked on Linux.

[breiler]

Nice, thanks!

Can you move the RequestFocusListener to the package com.willwinder.universalgcodesender.uielements.components and also add a comment that credits the original source, something like:

/**
 * Used for focusing the field in an JOptionDialog. 
 * Source from: https://tips4java.wordpress.com/2010/03/14/dialog-focus/
 */
public class RequestFocusListener implements HierarchyListener {
...