While OpenRCT2 already had code to look up the Steam path on macOS and Linux, it didn't look in the correct directory. This meant that it wouldn't detect the presence of RCT2, even if the user had downloaded it via the Steam Console.
Clang-format sees the text behind `#pragma region` as code and formats it. Instead of stating the copyright and date there, it's now in the comment block right below it. The text "Copyright" is left in the `#pragma region` line, as clang-format sees it as a single identifier.
I took the opportunity to normalize the dates, and add the copyright notice to the source files where it was missing them (except for third-party and the generated resources.h file).
This aims to make future refactoring easier. The arguments are removed where possible, but kept and marked with C++17's [[maybe_unused]] where they could not be removed (e.g. when they are used as a callback, rather than called directly).
I've skipped the rides/<category>/* and peep/* source files, because the rides source files are mostly generated and have a ton of unused variables, and the peep source files are being refactored.
I've also skipped most of window/* source files, because most of the functions are used as callbacks and will be bulk-renamed at some point.
