[clang-tools-extra] Add refactoring tool to convert between ternary (?:) expressions and equivalent if/else statements (PR #166822)

[Yanzuo Liu via cfe-commits]

zwuis wrote:

FYI, https://clang.llvm.org/extra/clang-tidy/Contributing.html is useful for writing clang-tidy checks.

https://github.com/llvm/llvm-project/pull/166822