[clang] [flang] [flang][draft] Improve debug info generation. (PR #84202)

[via cfe-commits]

jeanPerier wrote:

Great to see work on debug info, thanks!

I am in line with @tblah that we should aim at generating it from FIR/HLFIR as much as possible. For types, as Tom mentioned,  fir.type_info could be updated to be created with the type declaration location if it is not already the case.

Variable names that are meant to be reversible (there are [APIs to demangle](https://github.com/llvm/llvm-project/blob/d36d805373c27103edf13164260ef679efd30dc1/flang/include/flang/Optimizer/Support/InternalNames.h#L135)), so it would seems reasonable to me to start by using this for to identify Module variables.

+1 for a design doc/RFC on the topic.

https://github.com/llvm/llvm-project/pull/84202