_RawAutocompleteState.dispose() removes _updateOptionsViewVisibility
from the external FocusNode but forgets to remove _onFocusChange. When
the state is recreated with the same FocusNode both listeners accumulate,
and the second hide() call hits the _zOrderIndex != null assertion in
overlay.dart:1681. This is a Flutter framework bug, not a test deficiency.
Restore the filter with a comment pointing to the root cause so it can
be removed when we upgrade past the fix.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
