[clang] [clang][dataflow] Introduce a helper class for handling record initializer lists. (PR #86675)

[Yitzhak Mandelbaum via cfe-commits]

================
@@ -744,6 +744,35 @@ RecordStorageLocation *getBaseObjectLocation(const MemberExpr &ME,
 std::vector<const FieldDecl *>
 getFieldsForInitListExpr(const InitListExpr *InitList);
 
+/// Helper class for initialization of a record with an `InitListExpr`.
+/// `InitListExpr::inits()` contains the initializers for both the base classes
+/// and the fields of the record; this helper class separates these out into two
+/// different lists. In addition, it deals with special cases associated with
+/// unions.
+class RecordInitListHelper {
----------------
ymand wrote:

Why an object vs something like:
```
struct RecordInits {
  SmallVector<std::pair<const CXXBaseSpecifier *, Expr *>> BaseInits;
  SmallVector<std::pair<const FieldDecl *, Expr *>> FieldInits;
};
RecordInits RecordInitListHelper(const InitListExpr *InitList);
```

Is it because of the optional storage  needed for the union?

https://github.com/llvm/llvm-project/pull/86675