Run clang-format on all files

[rachel-fenichel]

Is your feature request related to a problem? Please describe.

Auto-formatting and consistent style are both valuable.

Describe the solution you'd like

Run clang-format on all files in the repository during Q3, while we are touching most of our files.

Describe alternatives you've considered

Continue to do this at the developer level, and only on changed files.

Additional context

#4569