Utils: Introduce a FilePath::withNewPath() convenience method

It's effectively the mirrored version of onDevice() with an
equally odd name which is a bit more straightforward to use
in some cases.

Change-Id: I0cfedeb58871a857c93144e2a0d734bad1bcd887
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/utils/fileutils.h

@@ -113,6 +113,7 @@ public:
 
     QString toString() const;
     FilePath onDevice(const FilePath &deviceTemplate) const;
+    FilePath withNewPath(const QString &newPath) const;
 
     QFileInfo toFileInfo() const;
     QVariant toVariant() const;