ComboBox and Spinner: no longer use preferred height for arrow button width, because preferred height may be zero, which would hide arrow button (see https://github.com/scijava/scijava-ui-swing/issues/77#issuecomment-1261452712)

- arrow button width depends on combobox/spinner height
- default/max button width is height of a raw combobox/spinner (without insets)
- min button width is 3/4 of default button width

CHANGELOG.md

@@ -1,6 +1,14 @@
 FlatLaf Change Log
 ==================
 
+## 3.0-SNAPSHOT
+
+#### Fixed bugs
+
+- ComboBox and Spinner: Fixed missing arrow buttons if preferred height is zero.
+  Minimum width of arrow buttons is 3/4 of default width.
+
+
 ## 2.5
 
 #### New features and improvements