Applying clang-format to the entire repository?

[ksuther]

Is this project open to using clang-format to format entire repository? We're working within our own fork and the inconsistent formatting style is an impediment to easily merging, rebasing, and eventually upstreaming changes.

There's already a .clang-format file in the repo that doesn't appear to be used (https://github.com/gnustep/libs-base/blob/master/.clang-format). If we can get a format that everyone agrees on then we can add pre-commit and tie it in to GitHub Actions to keep the style in place.

We're willing to do the work and submit a PR, but we don't want to go down that road this if it won't be accepted.