[clang-tools-extra] [clang-tidy] Add `readability-redundant-nested-if` check (PR #181558)

[Baranov Victor via cfe-commits]

vbvictor wrote:

Thanks for addressing the feedback and pinging.
Unfortunately now with more AI-assisted contributions burden on OSS maintainers has risen [link](https://discourse.llvm.org/t/concerns-about-influx-of-ai-generated-bug-fixes/90381) (in clang-tidy particularly many people start writing new checks). I can't keep up with backlog and decided to shift focus on bugfixes and then review new checks if time permits.
 I believe this check is valuable so I hope get back to it and land before 23 release.


https://github.com/llvm/llvm-project/pull/181558