Update C# signal documentation and remove bind array

- Updates C# signal documentation and code examples to the new API in 4.0
- Replace all `nameof` usages with the exposed `StringName`

doc/classes/Callable.xml

@@ -18,17 +18,19 @@
 		    callable.call("invalid")  # Invalid call, should have at least 2 arguments.
 		[/gdscript]
 		[csharp]
-		public void PrintArgs(object arg1, object arg2, object arg3 = null)
+		// Default parameter values are not supported.
+		public void PrintArgs(Variant arg1, Variant arg2, Variant arg3 = default)
 		{
 		    GD.PrintS(arg1, arg2, arg3);
 		}
 
 		public void Test()
 		{
-		    Callable callable = new Callable(this, nameof(PrintArgs));
-		    callable.Call("hello", "world"); // Prints "hello world null".
+		    // Invalid calls fail silently.
+		    Callable callable = new Callable(this, MethodName.PrintArgs);
+		    callable.Call("hello", "world"); // Default parameter values are not supported, should have 3 arguments.
 		    callable.Call(Vector2.Up, 42, callable); // Prints "(0, -1) 42 Node(Node.cs)::PrintArgs".
-		    callable.Call("invalid"); // Invalid call, should have at least 2 arguments.
+		    callable.Call("invalid"); // Invalid call, should have 3 arguments.
 		}
 		[/csharp]
 		[/codeblocks]