Utils: Split off file access interface from IDevice

The file accessing functions form now a class hierarchy by themselves,
the devices return a suitable point.

The previous implementation was mildly confusing by the special handling
of the DesktopDevice, fallbacks and remote cases in the same function
leading to unnecessary boilerplate when adding new functions and
codepaths that sometimes passed the FilePath API twice.

Implemented are a "DesktopDeviceFileAccess" taking care of the
previous !needsDevice() branches and a "UnixDeviceFileAccess"
covering the current docker and RL uses.

As a side-effect this unifies to a large degree the current docker
and RL code paths with were occasionally deviating from each other
while they shouldn't.

Change-Id: I4ff59d4be2a07d13e2ca5e9ace26a84160a87c9d
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/libs/utils/fileutils.h

@@ -86,13 +86,6 @@ public:
 
     static FilePaths toFilePathList(const QStringList &paths);
 
-    static void iterateUnixDirectory(
-            const FilePath &base,
-            const FileFilter &filter,
-            bool *useFind,
-            const std::function<RunResult(const CommandLine &)> &runInShell,
-            const FilePath::IterateDirCallback &callBack);
-
     static qint64 bytesAvailableFromDFOutput(const QByteArray &dfOutput);
 
     static FilePathInfo filePathInfoFromTriple(const QString &infos);