Contributes to https://github.com/flutter/flutter/issues/130459
It adds a test for
- `examples/api/lib/rendering/sliver_grid/sliver_grid_delegate_with_fixed_cross_axis_count.0.dart`
- `examples/api/lib/rendering/sliver_grid/sliver_grid_delegate_with_fixed_cross_axis_count.1.dart`
I also fixed a mistake in the documentation
Move `scroll_direction.0_test.dart` & `growth_direction.0_test.dart` to same directory structure as the example files.
Tests were already present, only had to move them & remove the entries from the missing tests.
Part of #130459
