VCS: Use more FilePath in ShellCommand and surroundings

Change-Id: Ie8c5fac09b45a54bcbe9a876044b653e7fccede5
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/vcsbase/vcsbaseclient.h

@@ -80,7 +80,7 @@ public:
                               JobOutputBindMode mode = NoOutputBind) const;
 
     void enqueueJob(VcsCommand *cmd, const QStringList &args,
-                    const QString &workingDirectory = QString(),
+                    const Utils::FilePath &workingDirectory = {},
                     const Utils::ExitCodeInterpreter &interpreter = {}) const;
 
     virtual Utils::Environment processEnvironment() const;