Submit changes to upstream Vim

[axvr]

We should consider submitting the latest changes for inclusion in Vim soon (preferably sometime before Vim 9 is released).

For this we will need to:

1. merge all open PRs which we want included,
2. test for regressions (I haven't found any yet),
3. write a summary of the included changes,
4. generate the patch (there is a comment in generate.clj on how to do this),
5. send the patch and summary (with a mention of the maintainership change) to the Vim-dev mailing list (+ CC @guns in the email),
6. await feedback.

NOTE: apparently it is now possible to open a pull request in the Vim GitHub repository instead of sending an email as that will automatically send the email and run the CI tests.

Open questions:

1. Should we also submit these changes to Neovim? (Does Neovim do it the same way?)

[axvr]

See PR vim/vim#7830.

Edit: merged in vim/vim@942db23