SaveData: Fix writer selection when multiple writers share the same extension

Previously, when multiple writers supported the same file extension, ParaView would always select the first available writer, regardless of the user's choice in the file dialog. This caused the IOSSWriter to be used instead of the LegacyExodusIIWriter when saving Exodus files, even when LegacyExodusIIWriter was explicitly selected.

This has been resolved by properly passing the selected writer from the FileDialog to vtkSMWriterFactory::CreateWriter, ensuring the user's choice is respected.

Additionally, an issue has been fixed where LegacyExodusIIWriter (the plugin-based wrapper for ExodusIIWriter) was not being instantiated properly, preventing it from being used even when selected.