xdemos: misc formatting cleanups

Here's some patches to try to make the code-style more consistent for the src/xdemos folder.

I'm trying to gradually clean up things so we hopefully eventually can use something like clang-format to enforce the correct code-style for each part of the repo.

This kind of ties in with the approach from !141, but I'm trying to go the other way around; first try to make the transformations that makes sense for consistency, and then define what the rules are. I hope this will lead to less needless churn, but this kind of work is pretty churn-heavy regardless. And yes, in case you wonder... clang-format did most of the heavy lifting here, I just picked the bits I wanted for each commit etc.