[clang] [Clang][C++26] Implement Pack Indexing (P2662R3). (PR #72644)

[Erich Keane via cfe-commits]

================
@@ -1685,7 +1685,12 @@ enum CXCursorKind {
    */
   CXCursor_CXXParenListInitExpr = 155,
 
-  CXCursor_LastExpr = CXCursor_CXXParenListInitExpr,
+  /**
+   *  Represents a C++26 pack indexing expression
----------------
erichkeane wrote:

```suggestion
   *  Represents a C++26 pack indexing expression.
```

https://github.com/llvm/llvm-project/pull/72644