Move CS9036 to compiler-messages folder and update TOC

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

Author: Copilot

docs/csharp/language-reference/compiler-messages/cs9036.md

@@ -0,0 +1,66 @@
+---
+description: "Compiler Error CS9036"
+title: "Compiler Error CS9036"
+ms.date: 05/19/2023
+f1_keywords: 
+  - "CS9036"
+helpviewer_keywords: 
+  - "CS9036"
+---
+# Compiler Error CS9036
+
+Required member 'memberName' must be assigned a value, it cannot use a nested member or collection initializer.
+
+When initializing an object with a `required` member, you must directly assign the member a value. You cannot use a nested member or collection initializer to set properties of the `required` member without first instantiating it.
+
+## Example
+
+The following sample generates CS9036:
+
+```csharp
+class C
+{
+    public string? Prop { get; set; }
+}
+
+class Program
+{
+    public required C C { get; set; }
+    
+    static void Main()
+    {
+        var program = new Program()
+        {
+            // error CS9036: Required member 'Program.C' must be assigned a value, it cannot use a nested member or collection initializer.
+            C = { Prop = "a" }
+        };
+    }
+}
+```
+
+## Solution
+
+To fix this error, directly assign a new instance of the required property and initialize its members:
+
+```csharp
+class C
+{
+    public string? Prop { get; set; }
+}
+
+class Program
+{
+    public required C C { get; set; }
+    
+    static void Main()
+    {
+        var program = new Program()
+        {
+            // Correct: Assign a new instance of C and then initialize its Prop property
+            C = new C { Prop = "a" }
+        };
+    }
+}
+```
+
+For more information on required members, see the [required modifier](../language-reference/keywords/required.md) reference article and [Object and Collection Initializers](../programming-guide/classes-and-structs/object-and-collection-initializers.md) guide.

docs/csharp/language-reference/toc.yml

@@ -1984,6 +1984,8 @@ items:
       href: ./compiler-messages/cs8812.md
     - name: CS8515
       href: ./compiler-messages/cs8515.md
+    - name: CS9036
+      href: ./compiler-messages/cs9036.md
     - name: CS9043
       href: ./compiler-messages/cs9043.md
   - name: Level 1 warning messages