Simplify C# print methods

- Extracts the parameters logic to a single method
- Simplify the handling of null parameters

(cherry picked from commit ad460cde7988e42acd4ec8d7c35d9c50f7c063a7)

modules/mono/glue/GodotSharp/GodotSharp/Core/GD.cs

@@ -46,6 +46,16 @@ namespace Godot
             return ret;
         }
 
+        private static object[] GetPrintParams(object[] parameters)
+        {
+            if (parameters == null)
+            {
+                return new[] { "null" };
+            }
+
+            return Array.ConvertAll(parameters, x => x?.ToString() ?? "null");
+        }
+
         public static int Hash(object var)
         {
             return godot_icall_GD_hash(var);
@@ -83,7 +93,7 @@ namespace Godot
 
         public static void Print(params object[] what)
         {
-            godot_icall_GD_print(Array.ConvertAll(what ?? new object[] { "null" }, x => x != null ? x.ToString() : "null"));
+            godot_icall_GD_print(GetPrintParams(what));
         }
 
         public static void PrintStack()
@@ -93,22 +103,22 @@ namespace Godot
 
         public static void PrintErr(params object[] what)
         {
-            godot_icall_GD_printerr(Array.ConvertAll(what ?? new object[] { "null" }, x => x != null ? x.ToString() : "null"));
+            godot_icall_GD_printerr(GetPrintParams(what));
         }
 
         public static void PrintRaw(params object[] what)
         {
-            godot_icall_GD_printraw(Array.ConvertAll(what ?? new object[] { "null" }, x => x != null ? x.ToString() : "null"));
+            godot_icall_GD_printraw(GetPrintParams(what));
         }
 
         public static void PrintS(params object[] what)
         {
-            godot_icall_GD_prints(Array.ConvertAll(what ?? new object[] { "null" }, x => x != null ? x.ToString() : "null"));
+            godot_icall_GD_prints(GetPrintParams(what));
         }
 
         public static void PrintT(params object[] what)
         {
-            godot_icall_GD_printt(Array.ConvertAll(what ?? new object[] { "null" }, x => x != null ? x.ToString() : "null"));
+            godot_icall_GD_printt(GetPrintParams(what));
         }
 
         public static float Randf()