List, Table and Tree: added colors for drag-and-drop

- added "enable drag and drop" checkbox to Demo on "Data Components" tab
- support copying UI default values lazy

flatlaf-testing/src/main/resources/com/formdev/flatlaf/testing/FlatTestLaf.properties

@@ -27,6 +27,11 @@
 @cellFocusColor=#ff0000
 @icon=#afafaf
 
+@dropCellBackground=#f00
+@dropCellForeground=#0f0
+@dropLineColor=#00f
+@dropLineShortColor=#ff0
+
 
 #---- globals ----