Change lazer's valid filename method to match stable

[peppy]

• Closes Beatmaps with certain characters in artist/title/difficulty name may cease to be updatable in stable after lazer submission #33060.
• Closes Uploading Beatmaps through Lazer creates a new difficulty on the web and deletes old difficulty #33421.
• Probably fixes the core breakage behind [Client & osu!web] Unsupported file type check and server updates before client finishes up #32001.

On revisiting the issue at hand, this honestly seems like the best way forward. It also addresses my concerns that with the method we were using, filenames could end up being half underscores.

The main reason for choosing to change the lazer end is that stable's difficulty update process is based on sending the beatmap's filename to the server. This means that if we use a proposed fix of checking online ID, it will still mean beatmaps cannot be updated on stable (for all users which have downloaded the beatmap) if a mapper updates once on lazer.

Implementation inspired by:

• https://referencesource.microsoft.com/#mscorlib/system/io/path.cs,1144ad3c4eff3f24
• https://github.com/peppy/osu-stable-reference/blob/996648fba06baf4e7d2e0b248959399444017895/osu!/GameplayElements/Beatmaps/Beatmap.cs#L1575-L1590

[bdach]

This means that if we use a proposed fix of checking online ID, it will still mean beatmaps cannot be updated on stable (for all users which have downloaded the beatmap) if a mapper updates once on lazer.

I'm not opposed to the direction but I don't understand this part.

[bdach]

I'm just going to buy this diff wholesale because it fixes issues like #33421, which I can claim because @wuaht is the first of many people who actually produced coherent reproduction steps other than "I didn't do nothing".

The reason that this fixes such issues is that preserving the filename matters for lazer too, because if a beatmap made in lazer is downloaded to stable, then modified there, saved, and exported, all of the filenames get rewritten to stable's convention. Then, on re-importing that export back to lazer, lazer only checks the md5 and the filename of the map. The id is not checked because mappers have been known to do broken crap like reuse online IDs to fix submission failures which means the online ID cannot be trusted for anything.

Due to the above, changing the filename convention causes lazer to no longer associate the reimport with the online beatmap, therefore effectively making it a beatmap set with no status but actual beatmap ID inside, which is when all that "encountered id not assigned by server" crap starts and the rest follows.

Jesus wept.

[bdach]

I've pushed an xmldoc rewording in 257fec8, please make sure you're ok with it.

[peppy]

Sorry about that, missed the xmldoc. Looks good 👍 .