[clang] [clang-format] Add support for absl nullability macros (PR #130346)

[Owen Pan via cfe-commits]

https://github.com/owenca requested changes to this pull request.

Why should we  add those macros to the default list? Can't you use the [`AttributeMacros`](https://clang.llvm.org/docs/ClangFormatStyleOptions.html#attributemacros) option instead?

https://github.com/llvm/llvm-project/pull/130346