[clang] [llvm] [clang] Add "debug_transparent" attribute (PR #110188)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

For a new feature with no existing implementation/language specification, I want to see community input from people who want to use it, and understand the potential impact on other projects (in this context, debuggers).  There isn't any formal requirement that happens on Discourse, but it's the default.

(With the upcoming governance changes, we might institute more formal review standards for features.)

https://github.com/llvm/llvm-project/pull/110188