We often use game IDs in paths, so we should try to make sure path traversal is impossible in game IDs. Admittedly, doing any kind of real attack using the six bytes available in game IDs is unrealistic, but no game ID should contain non-alphanumeric or non-ASCII characters anyway. Might also fix https://bugs.dolphin-emu.org/issues/13982 by skipping converting between encodings for game IDs.
This had to be in the header back when it was templated, but 083faa8b made it not templated.
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.
Instead of comparing the game ID, revision, disc number and name, we can compare a hash of important parts of the disc including all the aforementioned data but also additional data such as the FST. The primary reason why I'm making this change is to let us catch more desyncs before they happen, but this should also fix https://bugs.dolphin-emu.org/issues/12115. As a bonus, the UI can now distinguish the case where a client doesn't have the game at all from the case where a client has the wrong version of the game.