CppEditor: Move renameFilesForSymbol() to ProjectExplorer

We'd like to use it outside of CppEditor in the future.

Change-Id: Ie7553a17aa1d86fb898eaa315a1613ac0ff6b452
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cppeditor/cpptoolsreuse.cpp

@@ -9,6 +9,7 @@
 #include "cppcompletionassist.h"
 #include "cppeditorconstants.h"
 #include "cppeditorplugin.h"
+#include "cppfilesettingspage.h"
 #include "cpphighlighter.h"
 #include "cppqtstyleindenter.h"
 #include "cppquickfixassistant.h"
@@ -614,6 +615,11 @@ void openEditor(const Utils::FilePath &filePath, bool inNextSplit, Utils::Id edi
                                                               : EditorManager::NoFlags);
 }
 
+bool preferLowerCaseFileNames()
+{
+    return Internal::CppEditorPlugin::fileSettings()->lowerCaseFiles;
+}
+
 namespace Internal {
 
 void decorateCppEditor(TextEditor::TextEditorWidget *editor)