Co-authored-by: Wansmer <wansmer@gmail.com>
Co-authored-by: Andrew Voynov <andrewvoynov.b@gmail.com>
Co-authored-by: David Moberg <david.moberg@mediatek.com>

Problem:    E1135 is used for two different errors.
Solution:   Renumber one error.

https://github.com/vim/vim/commit/806da5176e9e9ab011d927c4ca33a8dde1769539

Co-authored-by: Bram Moolenaar <Bram@vim.org>

Problem:    Making a mapping work in all modes is complicated.
Solution:   Add the <Cmd> special key. (Yegappan Lakshmanan, closes vim/vim#7282,
            closes 4784, based on patch by Bjorn Linse)

https://github.com/vim/vim/commit/957cf67d50516ba98716f59c9e1cb6412ec1535d

Change docs to match Vim if it's wording is better.
Change error numbers to match Vim.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

helpers.source() was a hack to work around the lack of anonymous
:source. Its "create tempfile" behavior is not a required part of most
tests that use it.

Some tests still need the old "create tempfile" behavior either because
they test SID behavior, or because of missing nvim_exec features: #16071

In vim, scrolling a window might mess up the cmdline. To keep it simple,
cmdline was always cleared for any window scroll. In nvim, where safe scrolling
is implemented in the TUI layer, this problem doesn't exist.

Clearing the message on scrolling, when we not do it e.g when switching tabs
is a bit weird, as the former is a much smaller context change.

A vim patch introduced the possibility to avoid the cmdlline clear for
redraws caused by async events. This case will now trivially be covered,
as the redraw is always avoided.

vim-patch:8.0.0592: if a job writes to a buffer screen is not updated