These were just added to avoid churn when changing the default
of 'display'. To simplify message handling logic, we might want
to remove support for printing messages in default_grid later on.
This would allow things like printing error messages safely in the
middle of redraw, or a future graduation of the 'multigrid' feature.

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:    Ex command error cannot contain an argument.
Solution:   Add ex_errmsg() and translate earlier.  Use e_trailing_arg where
            possible.
https://github.com/vim/vim/commit/8930caaa1a283092aca81fdbc3fcf15c7eadb197

Remove duplicate test file 062_tab_pages_spec.lua

fixes #13078

Co-authored-by: Yuta Katayama <8683947+yutkat@users.noreply.github.com>

Avoid expect_exit, session will be closed when a new one is spawned.

Problem:
Since right-click can now show a popup menu, we can provide messaging to
guide users who expect 'mouse' to be disabled by default. So 'mouse' can
now be enabled by default.

Solution:
Do it.
Closes #15521