ICore: Change some path API to use FilePath

Change-Id: Id841d6177206a021c9e606ce560b47d1ae6e52b9
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/cpptools/compileroptionsbuilder.cpp

@@ -303,7 +303,7 @@ void CompilerOptionsBuilder::insertWrappedMingwHeaders()
 static QString creatorResourcePath()
 {
 #ifndef UNIT_TESTS
-    return Core::ICore::resourcePath();
+    return Core::ICore::resourcePath().toString();
 #else
     return QDir::toNativeSeparators(QString::fromUtf8(QTC_RESOURCE_DIR ""));
 #endif