[clang] [clang][Sema] Fix rejected-valid for explicit object parameters in dependent nested classes context (PR #209107)

[Corentin Jabot via cfe-commits]

================
@@ -1170,6 +1170,19 @@ struct S {
 };
 }
 
+namespace GH136472 {
+template<class T>
+struct S {
+  struct Nested {
+      void f(this auto);
+  };
+};
+
+// Test that out-of-line member defination of dependent nested class works
----------------
cor3ntin wrote:

```suggestion
// Test that out-of-line member definition of dependent nested class works
```

https://github.com/llvm/llvm-project/pull/209107