Apply clang-format universally.

* It is tough to contribute to a project that doesn't use a formatter,
* It is extra hard to contribute to a project which has configured the formatter, but ignores it for some files
* Code formatting makes it harder to hide obscure / weird bugs by accident or on purpose,

Let's rip the bandaid off?

Note that PRs currently in flight should be able to be merged relatively easily by applying `clang-format` to their tip prior to merge.

Co-authored-by: Graham Christensen <graham@grahamc.com>

src/libexpr-tests/nix_api_expr.cc

@@ -394,6 +394,7 @@ static void primop_bad_return_thunk(
 {
     nix_init_apply(context, ret, args[0], args[1]);
 }
+
 TEST_F(nix_api_expr_test, nix_expr_primop_bad_return_thunk)
 {
     PrimOp * primop =