Apply clang-format

What does this implement/fix?

Apply clang-format to the whole code base in one commit. I ran this precise command, and I had to run it several times find Eigen unsupported/Eigen -name "*" ! -name "*.txt" -type f -print0 | xargs -0 -n 1 clang-format -i --verbose.

This is because some of the files have long macro definitions that need to split over multiple lines, and clang-format will only split one line on each run.