[clang] Reapply "[Clang][CWG1815] Support lifetime extension of temporary created by aggregate initialization using a default member initializer" (PR #97308)

[Vlad Serebrennikov via cfe-commits]

================
@@ -206,19 +206,28 @@ namespace cwg1814 { // cwg1814: yes
 #endif
 }
 
-namespace cwg1815 { // cwg1815: no
+namespace cwg1815 { // cwg1815: 19
----------------
Endilll wrote:

Seems to be the case, yeah.
>From what I see, this effort was started back before 19 has branched, and was never backported to 19 branch.

https://github.com/llvm/llvm-project/pull/97308