Address feedback: use expression-bodied members, update syntax, and target .NET 9

Co-authored-by: BillWagner <[email protected]>

Author: Copilot

docs/csharp/language-reference/keywords/abstract.md

@@ -19,7 +19,7 @@ Abstract classes can contain both abstract members (which have no implementation
 
 The following example demonstrates an abstract class that contains both implemented methods and abstract members:
 
-[!code-csharp[AbstractWithImplemented](snippets/abstract/Program.cs#snippet1)]
+:::code language="csharp" source="snippets/abstract/Program.cs" id="snippet1":::
 
 In this example, the `Vehicle` abstract class provides:
 - **Implemented members**: `GetInfo()` method, `StartEngine()` method, and constructor - these provide common functionality for all vehicles

docs/csharp/language-reference/keywords/snippets/abstract/Program.cs

@@ -10,16 +10,10 @@ public Vehicle(string brand)
     }
 
     // Implemented method - provides functionality that all vehicles share
-    public string GetInfo()
-    {
-        return $"This is a {_brand} vehicle.";
-    }
+    public string GetInfo() => $"This is a {_brand} vehicle.";
 
     // Another implemented method
-    public virtual void StartEngine()
-    {
-        Console.WriteLine($"{_brand} engine is starting...");
-    }
+    public virtual void StartEngine() => Console.WriteLine($"{_brand} engine is starting...");
 
     // Abstract method - must be implemented by derived classes
     public abstract void Move();
@@ -33,10 +27,7 @@ public class Car : Vehicle
     public Car(string brand) : base(brand) { }
 
     // Implementation of abstract method
-    public override void Move()
-    {
-        Console.WriteLine($"{_brand} car is driving on the road.");
-    }
+    public override void Move() => Console.WriteLine($"{_brand} car is driving on the road.");
 
     // Implementation of abstract property
     public override int MaxSpeed => 200;
@@ -47,10 +38,7 @@ public class Boat : Vehicle
     public Boat(string brand) : base(brand) { }
 
     // Implementation of abstract method
-    public override void Move()
-    {
-        Console.WriteLine($"{_brand} boat is sailing on the water.");
-    }
+    public override void Move() => Console.WriteLine($"{_brand} boat is sailing on the water.");
 
     // Implementation of abstract property
     public override int MaxSpeed => 50;

docs/csharp/language-reference/keywords/snippets/abstract/abstract.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net9.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>