Fix clang-tidy on CI and introduce .clang-tidy file

This is a sister MR to !364 (merged), considering we are adding clang-format support in 0.49 why not get clang-tidy in as well? (The integration with the CI is sortof already present but only on linux and without a clang-tidy config file), the biggest advantage of using the config file is IDE integration.

The config is the one I usually start with from: https://github.com/cpp-best-practices/gui_starter_template but with the following checks disabled to better match the OpenMW style: readability-identifier-length, readability-braces-around-statements, hicpp-braces-around-statements; it enables a LOT more checks compared to the current CI ones, we should holdoff on it's usage in the CI as it will just spit out 10K+ warnings, but it can be used by devs to slowly increase code quality; clang-tidy can also be used to enforce naming styles: https://clang.llvm.org/extra/clang-tidy/checks/readability/identifier-naming.html but I did not set it up for the moment, maybe a senior dev can decide a good style and setup the settings later.