introduced Component.innerFocusWidth UI default to allow "inner" focus border (e.g. if outer focus border width is zero)

currently zero in all themes because:
- undecided whether it is necessary
- not useful for "Flat IntelliJ" and "Flat Darcula" themes
- focused buttons in "Flat Light" theme already have light blue background
- does not work for components in scrollpanes (e.g. textarea)

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatBorder.java

@@ -48,6 +48,7 @@ import javax.swing.text.JTextComponent;
  * {@link FlatUIUtils#paintParentBackground} to paint the empty space correctly.
  *
  * @uiDefault Component.focusWidth			int
+ * @uiDefault Component.innerFocusWidth		int
  * @uiDefault Component.focusColor			Color
  * @uiDefault Component.borderColor			Color
  * @uiDefault Component.disabledBorderColor	Color
@@ -59,6 +60,7 @@ public class FlatBorder
 	extends BasicBorders.MarginBorder
 {
 	protected final int focusWidth = UIManager.getInt( "Component.focusWidth" );
+	protected final int innerFocusWidth = UIManager.getInt( "Component.innerFocusWidth" );
 	protected final Color focusColor = UIManager.getColor( "Component.focusColor" );
 	protected final Color borderColor = UIManager.getColor( "Component.borderColor" );
 	protected final Color disabledBorderColor = UIManager.getColor( "Component.disabledBorderColor" );
@@ -76,7 +78,8 @@ public class FlatBorder
 
 			if( isFocused( c ) ) {
 				g2.setColor( getFocusColor( c ) );
-				FlatUIUtils.paintOutlineBorder( g2, x, y, width, height, focusWidth, lineWidth, arc );
+				FlatUIUtils.paintOutlineBorder( g2, x, y, width, height, focusWidth,
+					lineWidth + scale( (float) innerFocusWidth ), arc );
 			}
 
 			g2.setPaint( getBorderColor( c ) );

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatDarculaLaf.properties

@@ -26,6 +26,7 @@ Button.default.boldText=true
 #---- Component ----
 
 Component.focusWidth=2
+Component.innerFocusWidth=0
 Component.arrowType=triangle
 
 

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatIntelliJLaf.properties

@@ -39,6 +39,7 @@ CheckBox.icon.selectedPressedBackground=72A1D4
 #---- Component ----
 
 Component.focusWidth=2
+Component.innerFocusWidth=0
 Component.arrowType=triangle
 
 

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatLaf.properties

@@ -103,6 +103,7 @@ ComboBox.padding=2,6,2,6
 #---- Component ----
 
 Component.focusWidth=0
+Component.innerFocusWidth=0
 Component.arc=5
 Component.minimumWidth=64
 Component.arrowType=chevron