Print designation on list pattern (#877)

closes #876

Author: belav

Src/CSharpier.Generators/NodePrinterGenerator.sbntxt

@@ -9,7 +9,7 @@ namespace CSharpier.SyntaxPrinter
 {
     internal static class Node
     {
-        public static Doc Print(SyntaxNode syntaxNode, FormattingContext context)
+        public static Doc Print(SyntaxNode? syntaxNode, FormattingContext context)
         {
             if (syntaxNode == null)
             {

Src/CSharpier.Tests/FormattingTests/TestFiles/cs/ListPatterns.test

@@ -19,3 +19,10 @@ var someValue =
             var thirdCharacter,
             .. var rest
         ];
+
+return list switch
+{
+    [var elem] => elem * elem,
+    [] => 0,
+    [..] elems => elems.Sum(e => e + e),
+};

Src/CSharpier/SyntaxPrinter/SyntaxNodePrinters/ListPattern.cs

@@ -11,7 +11,9 @@ public static Doc Print(ListPatternSyntax node, FormattingContext context)
                 SeparatedSyntaxList.Print(node.Patterns, Node.Print, Doc.Line, context)
             ),
             Doc.SoftLine,
-            Token.Print(node.CloseBracketToken, context)
+            Token.Print(node.CloseBracketToken, context),
+            node.Designation is not null ? " " : Doc.Null,
+            Node.Print(node.Designation, context)
         );
     }
 }