feat(AutoCompleteBox): Add InnerLeftContent and InnerRightContent (#14610)

* feat: AutoCompleteBox InnerLeftContent

* fix: Address review

* fix: null annotation

* fix: merge nits

src/Avalonia.Controls/AutoCompleteBox/AutoCompleteBox.Properties.cs

@@ -173,6 +173,18 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<int> MaxLengthProperty =
             TextBox.MaxLengthProperty.AddOwner<AutoCompleteBox>();
 
+        /// <summary>
+        /// Defines the <see cref="InnerLeftContent"/> property
+        /// </summary>
+        public static readonly StyledProperty<object?> InnerLeftContentProperty =
+            TextBox.InnerLeftContentProperty.AddOwner<AutoCompleteBox>();
+
+        /// <summary>
+        /// Defines the <see cref="InnerRightContent"/> property
+        /// </summary>
+        public static readonly StyledProperty<object?> InnerRightContentProperty =
+            TextBox.InnerRightContentProperty.AddOwner<AutoCompleteBox>();
+
         /// <summary>
         /// Gets or sets the caret index
         /// </summary>
@@ -472,8 +484,7 @@ namespace Avalonia.Controls
             get => GetValue(ItemsSourceProperty);
             set => SetValue(ItemsSourceProperty, value);
         }
-        
-
+       
         /// <summary>
         /// Gets or sets the maximum number of characters that the <see cref="AutoCompleteBox"/> can accept.
         /// This constraint only applies for manually entered (user-inputted) text.
@@ -483,5 +494,23 @@ namespace Avalonia.Controls
             get => GetValue(MaxLengthProperty);
             set => SetValue(MaxLengthProperty, value);
         }
+      
+        /// <summary>
+        /// Gets or sets custom content that is positioned on the left side of the text layout box
+        /// </summary>
+        public object? InnerLeftContent
+        {
+            get => GetValue(InnerLeftContentProperty);
+            set => SetValue(InnerLeftContentProperty, value);
+        }
+
+        /// <summary>
+        /// Gets or sets custom content that is positioned on the right side of the text layout box
+        /// </summary>
+        public object? InnerRightContent
+        {
+            get => GetValue(InnerRightContentProperty);
+            set => SetValue(InnerRightContentProperty, value);
+        }      
     }
 }

src/Avalonia.Themes.Fluent/Controls/AutoCompleteBox.xaml

@@ -46,6 +46,8 @@
                      Margin="0"
                      DataValidationErrors.Errors="{TemplateBinding (DataValidationErrors.Errors)}"
                      MaxLength="{TemplateBinding MaxLength}"
+                     InnerLeftContent="{TemplateBinding InnerLeftContent}"
+                     InnerRightContent="{TemplateBinding InnerRightContent}"
                      />
             <Popup Name="PART_Popup" 
                    WindowManagerAddShadowHint="False"

src/Avalonia.Themes.Simple/Controls/AutoCompleteBox.xaml

@@ -19,7 +19,9 @@
                    CaretIndex="{TemplateBinding CaretIndex, Mode=TwoWay}"
                    DataValidationErrors.Errors="{TemplateBinding (DataValidationErrors.Errors)}"
                    Watermark="{TemplateBinding Watermark}"
-                   MaxLength="{TemplateBinding MaxLength}"
+                   MaxLength="{TemplateBinding MaxLength}"                   
+                   InnerLeftContent="{TemplateBinding InnerLeftContent}"
+                   InnerRightContent="{TemplateBinding InnerRightContent}"
                    />
 
           <Popup Name="PART_Popup"