Let :wincmd command accept a count like what its documentation suggests.
Previously it could only accept a range, which led to some ambiguity on
which attribute should be used when executing :wincmd using nvim_cmd.
Closes#19662.
Also fix a typo in a related Vim test:
vim-patch:9.0.0223: typo in diffmode test
Problem: Typo in diffmode test.
Solution: Fix the typo. (closesvim/vim#10932)
5fd6ab820b
