Get rid of QtcProcess::workingDirectory() overload

Adapt all callers' code so that it passes the FilePath
instead of QString. As a consequence introduce
TemporaryDirectory::masterDirectoryFilePath() and use
it where easily possible.

Change-Id: I14564949b3b916921e32a2957c84c03d1da43af2
Reviewed-by: hjk <hjk@qt.io>

src/plugins/languageclient/languageclientinterface.h

@@ -80,7 +80,7 @@ public:
 
     // These functions only have an effect if they are called before start
     void setCommandLine(const Utils::CommandLine &cmd);
-    void setWorkingDirectory(const QString &workingDirectory);
+    void setWorkingDirectory(const Utils::FilePath &workingDirectory);
 
 protected:
     void sendData(const QByteArray &data) final;