automate drag and drop cell reodering -- add new tests to existing `notebook-cell-reordering.test.ts`

[rodrigosf672]

@rodrigosf672 add automated tests for drag and drop. first check if they already partially exist elsewhere.

NOTE: notebook-cell-reordering.test.ts already exists but what I want here is to cover different features/approaches. The latter is more keyboard-based cell reordering, whereas the new test would be more focused on dragging.

Originally posted by @rodrigosf672 in #9840

[rodrigosf672]

do it in the same file, and hard.