ProjectExplorer: Use more FilePath in wizards, mostly JsonWizard*

JsonWizardFileGenerator's path member variables become FilePath and
GeneratedFile gets the QString based file setter and getter removed.

Also, a couple of other function parameters become FilePath. TODOs notes
added for further changes.

Change-Id: Ic4b791ed71c3c03adb8f15771e2dfa9af593abd8
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/coreplugin/generatedfile.h

@@ -42,8 +42,6 @@ public:
     ~GeneratedFile();
 
     // Full path of the file should be created, or the suggested file name
-    QString path() const;
-    void setPath(const QString &p);
     void setFilePath(const Utils::FilePath &p);
     Utils::FilePath filePath() const;