[clang] [clang] Add examples from [dcl.init.aggr] to C++ conformance tests (PR #91435)

[via cfe-commits]

================
@@ -0,0 +1,294 @@
+// RUN:  %clang_cc1 -std=c++2c -verify %s
+
----------------
cor3ntin wrote:

For future reference, can you say this is testing c++2c and maybe quote a paper number (latest working draft?)

https://github.com/llvm/llvm-project/pull/91435