[clang] [Clang] Fix AST dump for {CXXDefaultArgExpr, CXXDefaultInitExpr} (PR #88269)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

LGTM again, thanks for the extra work to get JSON dumping as well!

https://github.com/llvm/llvm-project/pull/88269