[clang] [flang] [flang][driver] Add pre-processing type to `.i` (pre-processed) files (PR #104664)

[Kareem Ergawy via cfe-commits]

ergawy wrote:

Ping! @banach-space did you manage to take another look? Please let me know if you disagree with my reply above or have further comments. 🙏 

https://github.com/llvm/llvm-project/pull/104664