4111: Fix filesystem/IO with unicode filenames on windows r=def- a=Robyt3
It was previously not possible to load a map or really any file with a filename containing unicode, e.g. german umlauts.
Now all filenames are converted from multibyte to widechar on windows, and the correct functions and structs (with the `W` suffix) are used consistently.
Some changes are made to synchronize ddnet's implementation with upstream (once https://github.com/teeworlds/teeworlds/pull/2936 has been merged there):
- The unused and not working `IOFLAG_RANDOM` is removed (on upstream ddnet's `IOFLAG_APPEND` is added instead).
- The `fs_listdir_info` function is renamed to `fs_listdir_fileinfo` and now using the parameter object `CFsFileInfo` that contains the filename, modified date and creation date, making it easier to add more properties in the future. `FS_LISTDIR_INFO_CALLBACK` is renamed to `FS_LISTDIR_CALLBACK_FILEINFO`.
## Checklist
- [X] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test if it works standalone, system.c especially
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)
Co-authored-by: Robert Müller <robert.mueller@uni-siegen.de>
