This runs build_tools/style.fish, which runs clang-format on C++, fish_indent on fish and (new) black on python.
If anything is wrong with the formatting, we should fix the tools, but automated formatting is worth it.
For usage in completion scripts.
Unlike `__fish_is_first_token` (which is probably not correctly named),
`__fish_is_first_arg` returns true regardless of whether existing tokens start with `-`
or not, to be used when an arg cannot be used with any other argument.
`__fish_prev_arg_in` is similar to `__fish_seen_...` but it explicitly
tests the preceding token only, for arguments that take only a single
parameter.
