Add FlatLaf as a L&F option

[tferr]

Suggestion for OptionsLookAndFeel:

Swing is for the most part abandonware, but Flatlaf has been making strides in patching several swing limitations, namely lack of consistent scaling in hiDPI screens (which is nasty on Linux). This is mainly an issue for Java 8 (as of today Java11 solves much of it, but it is not perfect. So this would still be relevant once Java11 is adopted).

Some motivations are laid out at the bottom of this comment: scijava/script-editor#56 (comment)

The tasks for this would be:

1. Adding FlatLaf as dependency
2. Make sure that initLookAndFeel() returns the FlatLlaf themes (i.e, FlatLightLaf.NAME, FlatIntelliJLaf.NAME, FlatDarkLaf.NAME, FlatDarculaLaf.NAME)
3. Have run() calling the Flatalaf setup(), something like:

	switch (lookAndFeelName) {
		case (FlatLightLaf.NAME):
			success = FlatLightLaf.setup();
			break;
		case (FlatIntelliJLaf.NAME):
			success = FlatIntelliJLaf.setup();
			break;
		case (FlatDarkLaf.NAME):
			success = FlatDarkLaf.setup();
			break;
		case (FlatDarculaLaf.NAME):
			success = FlatDarculaLaf.setup();
			break;
		default:
			(...) // existing logic
		}

[imagesc-bot]

This issue has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/shiny-new-script-editor/64160/38