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

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

(please note the update comment above, I did not read the change history and didn't realize the original patch was touching the common default style, not Google's style)

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