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

[Erich Keane via cfe-commits]

================
@@ -5697,6 +5698,39 @@ QualType ASTContext::getDecltypeType(Expr *e, QualType UnderlyingType) const {
   return QualType(dt, 0);
 }
 
+QualType ASTContext::getPackIndexingType(QualType Pattern, Expr *IndexExpr,
+                                         bool FullyExpanded,
+                                         ArrayRef<QualType> Expansions,
+                                         int Index) const {
+  QualType Canonical;
+  if (FullyExpanded && Index != -1) {
----------------
erichkeane wrote:

Yeah, I think 'partially substituted' or 'fully substituted' means what we want here.

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