Upgrade to clang-format-11 (and friends)

[cajun-rat]

At the moment Aktualizr uses clang-format-10 for formatting. We have to stick to one release to avoid different versions 'fighting' each other.

Debian Stable is currently on clang-format-11, but doesn't ship clang-format-10 which motivated me to look at an upgrade.

Aktualizr uses Ubuntu Focal (I think) for formatting checks, which has has clang-format-11.

From my initial trials, the only formatting that has changed is that Args &&... args will drop the second space to become Args &&...args

[pattivacek]

From my initial trials, the only formatting that has changed is that Args &&... args will drop the second space to become Args &&...args

Correct. And there are no changes from clang-format-11 and clang-format-12 by default. I don't particularly like the args change, and it's really annoying that there's no option for controlling it, and it's explicitly backwards-incompatible, so once we upgrade, anyone using older versions will conflict with the new version. Pretty bad work there, which is not usually what I expect from clang. (See here for some further insight.)

Anyway, at this point, it sounds like less of a pain to just upgrade and deal with it, since it's now causing problems to not upgrade.