Fix slow dialog box when opening a file

[charphi]

The file selection dialogue box can sometimes appear very slowly.
The problem seems to be related to the operating system, the network and the user's desktop shortcuts.

So far, the possible causes are a combination of the following:

• Windows OS
• Some disconnected network drives (such as disabled corporate VPN)
• Some links to these disconnected drives or to missing files

The cause could be the use of the operating system icon of a disconnected network drive from the current Swing Look&Feel.
This problem is difficult to reproduce and is often hidden by multiple layers of caches.

The class javax.swing.filechooser.FileSystemView seems to be the main source of problems. Expecially:

• FileSystemView#getChooserComboBoxFiles(): its result contains network drives on Windows
• FileSystemView#getChooserShortcutPanelFiles()
• FileSystemView#getSystemIcon(File)
• FileSystemView#getSystemIcon(File, int, int)
• FileSystemView#getSystemDisplayName(File)

[charphi]

For reference, I have created an issue at FlatLaf repository to find a better solution.
See JFormDesigner/FlatLaf#849