Using QFileSystemEntry::isAbsolute() broke handling of resource paths.
Extended QDir::absoluteFilePath() tests to cover absolute resource path
and some UNC variants also resolved in the same fix.
Amend existing filePath tests to use drives where needed.
Task-number: QTBUG-68337
Change-Id: I4f02cf67828ad93e562857118f8442037f18bab7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>