[clang] [clang] Add clang::default_constructed_after_move attribute (PR #178432)

[via cfe-commits]

juanvazquez wrote:

I've just published RFC in discourse: https://discourse.llvm.org/t/rfc-add-a-class-attribute-clang-null-after-move-for-use-after-move-analysis/89760

Hope all the required information for the RFC is there. If you miss something please don't hesitate to tell, either here or in the discourse topic.

If the RFC is accepted I'll restart the work on this pr having into account any feedback that may arise during the RFC.

https://github.com/llvm/llvm-project/pull/178432