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/libs/utils/qtcprocess.h

@@ -99,7 +99,6 @@ public:
 
     FilePath workingDirectory() const;
     void setWorkingDirectory(const FilePath &dir);
-    void setWorkingDirectory(const QString &dir); // FIXME: Kept to ease downstream transition
 
     void setUseCtrlCStub(bool enabled);
     void setLowPriority();