Restored child editor windows have no title

Child windows created as part of the editor startup process won't have a title. This happens because the native window hasn't yet been created when we set the title in FTabManager::RestoreArea_Helper, so the title setting fails and isn't retried after the native window is generated

1. Launch the editor. Ensure "Restore Open Asset Tabs on Restart is enabled, and the editor isn't being run through Visual Studio
2. Open a separate ContentBrowser window.
3. Relaunch the editor without closing the separate ContentBrowser window.
4. Observe the title in the windows os taskbar is blank for the newly created ContentBrowser window.