sceKernelMkdir checked that the parent of the resolved path exists, but
for "dir/" std::filesystem::path reports "dir" itself as the parent, so
the call failed with ENOENT and created nothing, while FreeBSD's mkdir
(and the POSIX mkdir export) accept it. Strip trailing separators first,
and report ENOTDIR when the parent exists but is not a directory.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit 5f74ddba8b346e6c552cf02554d47382708206f3)
3779ffa375