Add focused state for DropDownButton and reduces the icon width of the dropdown model button (#13773)

<!-- Please read CONTRIBUTING.md before submitting a pull request -->

Fixes #13766, #13765


## Proposed changes

- Added a Focused state to the property page's drop-down button.
- Reduces the icon width of the model button.


<!-- We are in TELL-MODE the following section must be completed -->

## Customer Impact

- The drop-down button of the Property page can be focused under
DarkMode

## Regression? 

- Yes 

## Risk

- Minimal

<!-- end TELL-MODE -->


## Screenshots <!-- Remove this section if PR does not change UI -->

### Before
Dropdown arrow and ellipse symbol in PropertyGrid appears larger in
DarkMode and the focus indicator (e.g., dotted line or outline) is not
visible when navigating to the DropDownButton or Ellipse Button controls
by keyboard

Dark mode on 100% DPI:
<img width="468" height="42" alt="image"
src="https://github.com/user-attachments/assets/7f556f54-f4d7-43bd-a37f-bb6722cc7c90"
/>

<img width="462" height="66" alt="image"
src="https://github.com/user-attachments/assets/29044324-78a6-4ae7-b396-10c8e1228d50"
/>

Dark mode on 250% DPI:
<img width="1377" height="112" alt="image"
src="https://github.com/user-attachments/assets/038bab90-10b9-4f9b-9d61-dde7ab72edb2"
/>

<img width="1391" height="106" alt="image"
src="https://github.com/user-attachments/assets/5427dd45-fba3-47ca-b9fe-6db0387df029"
/>



### After
The dropdown arrow appears normal and it can be focued

100% DPI:
<img width="468" height="63" alt="image"
src="https://github.com/user-attachments/assets/e2eadd54-eef3-4b62-a78e-8cf5d12eb176"
/>

<img width="493" height="82" alt="image"
src="https://github.com/user-attachments/assets/ce2250c8-bcd8-4d2c-b2ad-5abb4d6b394a"
/>


250% DPI:
<img width="857" height="120" alt="image"
src="https://github.com/user-attachments/assets/960221c6-e1cf-4645-b2fe-af9b638b7c0c"
/>

<img width="1112" height="171" alt="image"
src="https://github.com/user-attachments/assets/b589a411-a7d4-4c36-a873-2ca1359d0400"
/>



## Test methodology <!-- How did you ensure quality? -->

- manually
 

## Test environment(s) <!-- Remove any that don't apply -->

- .net 10.0.0-preview.7.25377.103


<!-- Mention language, UI scaling, or anything else that might be
relevant -->

###### Microsoft Reviewers: [Open in
CodeFlow](https://microsoft.github.io/open-pr/?codeflow=https://github.com/dotnet/winforms/pull/13773)

Author: LeafShi1

src/System.Windows.Forms/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+System.Windows.Forms.VisualStyles.ComboBoxState.Focused = 5 -> System.Windows.Forms.VisualStyles.ComboBoxState

src/System.Windows.Forms/System/Windows/Forms/Controls/PropertyGrid/PropertyGridInternal/DropDownButton.cs

@@ -83,14 +83,22 @@ protected override void OnPaint(PaintEventArgs pevent)
     {
         ComboBoxState state = ComboBoxState.Normal;
 
-        if (MouseIsDown)
+        if (!Enabled)
+        {
+            state = ComboBoxState.Disabled;
+        }
+        else if (MouseIsDown)
         {
             state = ComboBoxState.Pressed;
         }
         else if (MouseIsOver)
         {
             state = ComboBoxState.Hot;
         }
+        else if (Focused)
+        {
+            state = ComboBoxState.Focused;
+        }
 
         base.OnPaint(pevent);
 
@@ -101,6 +109,7 @@ protected override void OnPaint(PaintEventArgs pevent)
                 ComboBoxState.Disabled => ModernControlButtonState.Disabled,
                 ComboBoxState.Hot => ModernControlButtonState.Hover,
                 ComboBoxState.Pressed => ModernControlButtonState.Pressed,
+                ComboBoxState.Focused => ModernControlButtonState.Focused,
                 _ => ModernControlButtonState.Normal
             };
 

src/System.Windows.Forms/System/Windows/Forms/Rendering/ControlPaint.ModernControlButtonState.cs

@@ -10,6 +10,7 @@ internal enum ModernControlButtonState
         Normal,
         Disabled,
         Pressed,
-        Hover
+        Hover,
+        Focused
     }
 }

src/System.Windows.Forms/System/Windows/Forms/Rendering/ControlPaint_ModernControlButtonRenderer.cs

@@ -91,6 +91,8 @@ internal static void DrawModernControlButton(
 
             bool hasRoundedBorder = (button & ModernControlButtonStyle.RoundedBorder) != 0;
 
+            bool isFocused = state == ModernControlButtonState.Focused;
+
             // Draw background
             using (var backgroundBrush = backgroundColor.GetCachedSolidBrushScope())
             {
@@ -121,6 +123,14 @@ internal static void DrawModernControlButton(
                 }
             }
 
+            if (isFocused)
+            {
+                // Draw focus rectangle
+                Rectangle focusRect = bounds;
+                focusRect.Inflate(-1, -1); // Deflate to avoid drawing over the border
+                DrawFocusRectangle(graphics, focusRect, Color.Empty, backgroundColor);
+            }
+
             // Draw the content
             ModernControlButtonStyle contentType = button
                 & ~(ModernControlButtonStyle.SingleBorder
@@ -280,7 +290,7 @@ private static void DrawEllipseSymbol(Graphics graphics, Brush brush, int center
     {
         // Calculate dot size as a proportion of button height
         int minDimension = Math.Min(bounds.Width, bounds.Height);
-        int dotSize = Math.Max(1, (int)(minDimension * 0.15 * ContentScaleFactor));
+        int dotSize = Math.Max(1, (int)(minDimension * 0.1 * ContentScaleFactor));
 
         // Calculate proportional spacing
         int spacing = Math.Max(1, dotSize / 2);
@@ -310,7 +320,7 @@ private static void DrawEllipseSymbol(Graphics graphics, Brush brush, int center
     private static void DrawOpenDropDownChevron(Graphics graphics, Brush brush, int centerX, int centerY, int size)
     {
         // Calculate chevron dimensions proportionally
-        int chevronWidth = size + (size / 2);
+        int chevronWidth = size;
         int chevronHeight = (size * 2) / 3;
 
         // Stroke thickness scales with size

src/System.Windows.Forms/System/Windows/Forms/VisualStyles/ComboBoxState.cs

@@ -8,5 +8,6 @@ public enum ComboBoxState
     Normal = 1,
     Hot = 2,
     Pressed = 3,
-    Disabled = 4
+    Disabled = 4,
+    Focused = 5,
 }