Yellow squiggly lines begone! Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes. If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed. The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports. Not everything is removed, but the cleanup should be substantial enough. Because this done on Linux, code that isn't used on it is mostly untouched. (Hopefully no open PR is depending on these imports...)
In DITSpecification.cpp, MaterialAsset.cpp, and ShaderAsset.cpp, lambda predicates were replaced by pointers to member functions because ranges algorithms are able invoke those. In NetPlayClient.cpp, the non-trivial `NetPlay::Player` elements were being passed by value in `NetPlayClient::DoAllPlayersHaveGame()`. This has been fixed. In WIABlob.cpp, the second example's predicate was returning the `std::optional` by value instead of implicitly converting it to a bool. This has been fixed.
`Common::IsLower(char)` was omitted as nothing needed it.
SPDX standardizes how source code conveys its copyright and licensing information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX tags are adopted in many large projects, including things like the Linux kernel.