Make file system scan more robust

Previously, a change was missed if it happened while the scan was in progress and already past the affected location.

Also:
- Consider the scan changes thread on termination, in addition to the full scan one
- Add FS-reported hidden to the check for hidden by the editor file system

editor/editor_file_system.h

@@ -145,6 +145,7 @@ class EditorFileSystem : public Node {
 	bool scanning;
 	bool importing;
 	bool first_scan;
+	bool scan_changes_pending;
 	float scan_total;
 	String filesystem_settings_version_for_import;
 	bool revalidate_import_files;