Issues with dark modes

[Klumbumbus]

This is a collection of issues with dark mode, especially with FlatLaf Dark, reported before on different places. The reason might be in JOSM core, the FlatLaf plugin or the FlatLaf Laf itself.

• The text in the status bar is nearly unreadable --> see 3rd screenshot in #19027
• Blue links are hard to read --> ticket:19027#comment:24
• Boolean values with icons in menus are hard to see if checked or unchecked --> attachment:check_boxes_dark_mode.png​ (Windows LaF for comparison on the right, original reported in #19785)
• The warning message in the upload dialog looks not good (light orange background color) --> attachment:upload_dark_mode.png​ (original reported as ​facebook comment)