[clang] [llvm] [clang] Implement P3733R1 (PR #203944)

[Jan Schultke via cfe-commits]

eisenwave wrote:

Alright, I hope that fixes it.

I had to fix the unprintable string display problems in `LiteralSupport.cpp` as a drive-by because in `cwg26xx.cpp`, the test expectations would otherwise contain suggestions of `CR` and `FF`, which aren't printable, and that was just totally exploding.

https://github.com/llvm/llvm-project/pull/203944