Updates to the Code Style Guide

[eXpl0it3r]

• [ ] All/most of the code formatting rules can be replaced with information on how to run clang-tidy
• [ ] Add reference to enforced clang-tidy rules, see also https://github.com/SFML/SFML/blob/master/.clang-tidy
• [ ] Add a policy for pass-by-value for trivially copyable classes, see also https://github.com/SFML/SFML/issues/3047
• [ ] Add a policy for cast usage, see also https://github.com/SFML/SFML/pull/3061
• [ ] Add a policy about usage of auto, especially regarding type inference, see also https://github.com/SFML/SFML/pull/3067#discussion_r1630224712
• [ ] Add a policy regarding usage of struct vs class, see also https://github.com/SFML/SFML/pull/3165
• [ ] Add a policy regarding example code writing:
  • [ ] Define event model should be promoted by default
  • [ ] Define error handling when loading resources