[kio_file] Handle renaming file 'A' to 'a' on FAT32 filesystems
Summary: Use QFile::rename() to handle so renaming a dir/file 'A' to 'a' on case-insensitive filesystems, e.g. FAT32/VFAT.
This code used to be in CopyJob but now has found a new home in kio_file, see the diff review for more details.
Test Plan:
- jobtest unit test passes again
- Renaming a dir 'A' to 'a' on a FAT32 partition still works
Reviewers: #frameworks, dfaure
Subscribers: kde-frameworks-devel
Tags: #frameworks
Differential Revision: https://phabricator.kde.org/D29610