Relax paranoidal mount point locking and temp dir creation mechanism.
It was incompatible with a setup where user directory is symlinked.
Instead, create temp dir as close to target as possible (see savedata).
Clear() error checking simplified a bit
Mount() now clears cache if ID was changed from last or NULL specified.
Implemented vfs::host::remove_all():
Clear() now uses vfs::host::remove_all() to match behaviour on Windows with ps3
Possibly fixes sys_fs_rmdir and other cases of directory removal.
Make sure the directory with deleted files always becomes empty.
For this purpose, temp files are moved to the root of the device.
Preprocess . and .. correctly
Don't use recursive locking
Also use std::string_view
Fix format system for std::string and std::string_view
Fix fmt::merge for std::string_view
