[clang] [RFC][clang][AST] Copy default-member-init wherever it is used and add a tag to its initialization init-list node (PR #221299)

[Jan Voung via cfe-commits]

================

----------------
jvoung wrote:

Could you update the comment "use the overload that takes a `CXXThisExpr`" (now that the overload is removed)?

I wonder if the change in `VisitCXXThisExpr` where it first checks `getListInitObjectLocation` and then checks `getThisPointeeStorageLocation` should be inlined into here? Previously, we were only able to hook in to the one caller `VisitCXXThisExpr` to call the right overload (which I guess was okay because it was only needed while evaluating the list init).

https://github.com/llvm/llvm-project/pull/221299