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. (closes vim/vim#10932)
https://github.com/vim/vim/commit/5fd6ab820b4a0aaa5c6020852f39d118375fab49

Problem:    Invalid memory access in diff mode with "dp" and undo.
Solution:   Make sure the line number does not go below one.
https://github.com/vim/vim/commit/4e677b9c40ccbc5f090971b31dc2fe07bf05541d

Problem:    Test for DiffUpdated fails.
Solution:   Also accept a count of two.
https://github.com/vim/vim/commit/f65cc665fa751bad3ffe75f58ce1251d6695949f

Problem:    Invalid memory access after diff buffer manipulations.
Solution:   Use zero offset when change removes all lines in a diff block.
https://github.com/vim/vim/commit/c101abff4c6756db4f5e740fde289decb9452efa

Problem:    Crash when deleting buffers in diff mode.
Solution:   Recompute diffs later.  Skip window without a valid buffer.
https://github.com/vim/vim/commit/cd38bb4d83c942c4bad596835c6766cbf32e5195

Problem:    In diff mode windows may get out of sync. (Gary Johnson)
Solution:   Avoid that the other window scrolls for 'cursorbind'.
https://github.com/vim/vim/commit/a315ce1f326b836167ca8b1037dafd93eb8d4d4e

Problem:    No tests for clicking in the GUI tabline.
Solution:   Add test functions to generate the events.  Add tests using the
            functions. (Yegappan Lakshmanan, closes vim/vim#9638)
https://github.com/vim/vim/commit/b0ad2d92fd19e673ddbbc66742bae3f71778efde

This can avoid divergences from Vim in some small places.

Problem:    Diff mode confused by NUL bytes.
Solution:   Handle NUL bytes differently. (Christian Brabandt, closes vim/vim#9421,
            closes vim/vim#9418)
https://github.com/vim/vim/commit/06f6095623cfcc72da08748c058d13b465652fd4

Problem:    Using wrong highlight for cursor line number.
Solution:   Take filler lines into account when using CursorLineNr.
            (closes vim/vim#9897)
https://github.com/vim/vim/commit/127969cf98000a760826ca3a0f3781a8b79522f1