Wizards: Turn "platform" into an Id

It used to be a string constant.

Change-Id: Ibea34dc52e97a483989e6d628b908231f4e2dc54
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>

src/plugins/coreplugin/basefilewizardfactory.cpp

@@ -80,7 +80,7 @@ static int indexOfFile(const GeneratedFiles &f, const QString &path)
 */
 
 Utils::Wizard *BaseFileWizardFactory::runWizardImpl(const QString &path, QWidget *parent,
-                                                    const QString &platform,
+                                                    Id platform,
                                                     const QVariantMap &extraValues)
 {
     QTC_ASSERT(!path.isEmpty(), return 0);