Utils: Add FilePath::isSameFile()

FilePath::isSameFile() checks if two files are the same file.
It first checks if its on the same device. If it is, it will
try to read the fileId of the files and compare them.

Change-Id: I83668955cacd4e5ed03d43a3fee2be29e9d0a6f0
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/fileutils.h

@@ -81,7 +81,6 @@ public:
     static bool isAbsolutePath(const QString &fileName) { return !isRelativePath(fileName); }
     static FilePath commonPath(const FilePath &oldCommonPath, const FilePath &fileName);
     static FilePath commonPath(const FilePaths &paths);
-    static QByteArray fileId(const FilePath &fileName);
     static FilePath homePath();
 
     static FilePaths toFilePathList(const QStringList &paths);