Problem:    ":wincmd =" equalizes in two directions.
Solution:   Make ":vertical wincmd =" equalize vertically only and
            ":horizontal wincmd =" equalize horizontally only.
https://github.com/vim/vim/commit/21c3a80a7fd6b7fc250ce5dc287963511f54b86f

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:    The argument list may contain duplicates.
Solution:   Add the :argdedeupe command. (Nir Lichtman, closes vim/vim#6235)
https://github.com/vim/vim/commit/73a024209cbfbd5b39a2e974084d807c6131e2ed

Use latest index.txt :argdedupe doc from Vim.

Problem:    Cannot use :vimgrep in omni completion, causing C completion to
            fail.
Solution:   Add the EX_LOCK_OK flag to :vimgrep. (closes vim/vim#7292)
https://github.com/vim/vim/commit/33aecb1f2c85711d53858b71f5f3c2cbe076435f

Cherry-pick Test_resize_from_copen() indent change from patch 8.2.1432.

Problem:    Vim9: error when using vim9script in TextYankPost.
Solution:   Use EX_LOCKOK instead of the EX_CMDWIN flag for command that can
            be used when text is locked. (closes vim/vim#6529)
https://github.com/vim/vim/commit/37394ff75270877a032422abcd079a6732a29730

Problem:    Finding a user command is not optimal.
Solution:   Start further down in the list of commands.
https://github.com/vim/vim/commit/a494f56f885876c98a276f7acfa386bfbb344680

Problem:    No menus specifically for the terminal window.
Solution:   Add :tlmenu. (Yee Cheng Chin, closes vim/vim#3439) Add a menu test.
https://github.com/vim/vim/commit/4c5d815256099b50eca2ec5bf8f9aaa67a890211

ADDR_OHTER comes from patch 8.1.1241, which has already been ported.

Problem:    Can't use :popup for a menu in the terminal. (Wei Zhang)
Solution:   Make :popup work in the terminal.  Also fix that entries were
            included that don't work in the current state.
https://github.com/vim/vim/commit/29a2c08d792e4458a0af8371f5341394829fce29

Adds a Lua-only `preview` flag to user commands which allows the command to be incrementally previewed like `:substitute` when 'inccommand' is set.