added content for missing error message cs8125 (#31516)

* added content for missing error message cs8125

* Update docs/csharp/language-reference/compiler-messages/cs8125.md

Co-authored-by: Bill Wagner <[email protected]>

Author: peteraritchie

docs/csharp/language-reference/compiler-messages/cs8125.md

@@ -0,0 +1,39 @@
+---
+description: "Compiler Error CS8125"
+title: "Compiler Error CS8125"
+ms.date: 9/30/2022
+f1_keywords:
+  - "CS8125"
+helpviewer_keywords:
+  - "CS8125"
+---
+# Compiler Error CS8125
+
+Tuple element name is only allowed at position.
+
+## Example
+
+ The following sample generates CS8125:
+
+```csharp
+// CS8125.cs (2,15)
+
+public class C
+{
+    public void Method()
+    {
+        var tuple3 = (Item2: 2, Item1: 1);
+    }
+}
+```
+
+## To correct this error
+
+If tuple element names `Item1`, `Item2`, etc. are used, ensuring the correct order corrects this error:
+
+```csharp
+    public void Method()
+    {
+        var tuple3 = (Item1: 2, Item2: 1);
+    }
+```

docs/csharp/language-reference/compiler-messages/toc.yml

@@ -1605,6 +1605,8 @@ items:
     href: cs7003.md
   - name: CS8124
     href: cs8124.md
+  - name: CS8125
+    href: cs8125.md
   - name: CS8145
     href: cs8145.md
   - name: CS8146

docs/csharp/misc/sorry-we-don-t-have-specifics-on-this-csharp-error.md

@@ -296,7 +296,6 @@ f1_keywords:
   - "CS8121"
   - "CS8122"
   - "CS8123"
-  - "CS8125"
   - "CS8126"
   - "CS8127"
   - "CS8128"