[clang] [clang-format] Add IndentPPDirectives Leave option (PR #139750)

[Gedare Bloom via cfe-commits]

gedare wrote:

This change can help support some of the goals stated in #35368 but doesn't exactly capture the intent of that Issue, which adds a requirement to make the PP indent level also advance the indent level. I am not currently interested in that particular feature.

https://github.com/llvm/llvm-project/pull/139750