[.NET] Use collection expressions in docs

As of C# 12 we can now use collection expressions to reduce some boilerplate when initializing collections.

doc/classes/ArrayMesh.xml

@@ -25,16 +25,16 @@
 		m.mesh = arr_mesh
 		[/gdscript]
 		[csharp]
-		var vertices = new Vector3[]
-		{
+		Vector3[] vertices =
+		[
 		    new Vector3(0, 1, 0),
 		    new Vector3(1, 0, 0),
 		    new Vector3(0, 0, 1),
-		};
+		];
 
 		// Initialize the ArrayMesh.
 		var arrMesh = new ArrayMesh();
-		var arrays = new Godot.Collections.Array();
+		Godot.Collections.Array arrays = [];
 		arrays.Resize((int)Mesh.ArrayType.Max);
 		arrays[(int)Mesh.ArrayType.Vertex] = vertices;