[clang] Implement KeepEmptyLines.AtEndOfBlock feature (PR #224223)

[Arkadiusz Bokowy via cfe-commits]

arkq wrote:

@HazardyKnusperkeks, I saw that you've reviewed the last PR for the clang/lib/Format/Format.cpp path. Could you please taka a look at this new feature as well?

https://github.com/llvm/llvm-project/pull/224223