Use pre-commit to check C++ and Python formatting

pre-commit is a very practical tool to automatically run checks on the files to be committed to the repository.

This MR adds a pre-commit configuration that invokes clang-format and yapf to replace the home made ci-utils/check-formatting.

The only draw back is that the available versions of clang-format start from 10, so there is a minor difference in the output when using it instead of clang-format-8: the fixed the discrepancy between constructors invoked with parentheses and braces, so we get

std::string a( "a" );
std::string b{ "b" };

instead of

std::string a( "a" );
std::string b{"b"};

When we merge this, we can decide if to format everything or update the formatting only of the files we touch in each MR.

changed milestone to %v36r2

I think only the touched files in the MR should be formatted.

Then this MR does not need any extra work.

Do you mind reviewing/merging it, please?

assigned to @leggett

does this require python 3.8 for the venv?

not really... you need pre-commit so other versions should be fine. I picked one at random for the CI job.

approved this merge request

merged

mentioned in commit 57379798

mentioned in merge request !1286 (merged)

mentioned in issue lhcb/Moore#361

mentioned in merge request lhcb-core/LbDevTools!215 (merged)

mentioned in merge request lhcb/LHCb!4346 (merged)