Update runtime files
https://github.com/vim/vim/commit/23515b4ef7580af8b9d3b964a558ab2007cacda5

Omit filetype.txt changes for :Man.

Runtime file updates.
https://github.com/vim/vim/commit/664f3cf3f21d3699bfd179c318ef5c869c085648

Update runtime files.
https://github.com/vim/vim/commit/403f3eb4c1890826a5b3b5922c0e8e45be79a476

Port sr.po changes, done by vim-patch.sh.
No way I'm manually porting the rest.

Fix vim.desktop generation.
https://github.com/vim/vim/commit/1ebbb6ee452dfca89335ac75f07c3db133b56645

Update runtime files
https://github.com/vim/vim/commit/574ee7bc1246070dba598f9561a2776aa1a10d07

Omit ru.po because I don't know the language and there's too much to port.

Update runtime files
https://github.com/vim/vim/commit/96f45c0b6fc9e9d404e6805593ed1e0e6795e470

Omit de.po changes.
Same reason as before: too much and I don't understand the language.

Update runtime files
https://github.com/vim/vim/commit/8fe1000e9c3438d0ff36cf2340f0f0e48f8fb89f

Omit de.po changes.
There's too many lines to port and I don't understand the language.

Closes #3689

cmake: Add `desktop-install` and `icon-install` targets. `runtime`
target will trigger them.

Specification:
https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html#recognized-keys

Icons are stored system-wide in /usr/share/applications or user wide at
/usr/share/icons/hicolor/scalable/apps and can be overriden in ~/.local/share/icons

nvim.desktop file can be installed system wide or in
~/.local/share/applications/

To test without an installer:
$ xdg-desktop-menu install --novendor runtime/nvim.desktop
$ xdg-icon-resource install --novendor --mode user --size 64 contrib/nvim-icon.png

Once it is installed, you can test with gtk-launch if installed or
dmenu/rofi (drun mode)