Check if the return value of std::filesystem::remove_all is -1 rather
than 0; the former is the specified return value if there's an error
while 0 just means the directory already didn't exist (which is the end
result we want).

Previously error messages such as the following were possible:
E[COMMON]: DeleteDirRecursively: [path]/User/RedirectSession/ failed The
operation completed successfully.

Also adds a period in the error string to make it look nicer.

Logic and structures are largely taken from Linux source:
drivers/bluetooth/btusb.c
drivers/bluetooth/btrtl.c
drivers/bluetooth/btrtl.h

Unlike custom banners which work as an override, this mechanism works as
a fallback. The use case is if you have games you don't really play but
want to keep around for testing purposes without filling up your NAND
with lots of saves. For ease of use, the directory structure is the same
but only title/$title_hi/$title_lo/data/banner.bin files are
relevant.

It was being done manually, which a TODO comment advised against.
Using generic_string() from std::filesystem::path solves this.

Fix encoding issue using generic_wstring instead.

Badges are saved in /User/Cache/RetroAchievements on first download and reused from there instead of redownloaded.