[clang] [clang-repl] Lay the foundation of pretty printing for C. (PR #89811)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Generally looks good, but it seems that some parts of this PR are also incorporated into another PR, so it's a bit hard to review.

https://github.com/llvm/llvm-project/pull/89811