runtime(keymap): Add ukrainian-enhanced keymap

runtime(keymap): Add ukrainian-enhanced keymap

The "Ukrainian enhanced keymap" allows you to type Ukrainian in Vim
using jcuken Windows layout.

Original file is made by Ivan Korneliuk and can be found at
https://github.com/vansha/ukrainian-enhanced.vim. It is being added here
with the permission of the author.

There is another ukrainian layout already in Vim, namely the
keymap\ukrainian-jcuken.vim script by Anatoli Sakhnik. But this one
differs in way it maps numeric keys. It uses values usual for Windows
users.

closes: #16628

Signed-off-by: Vladyslav Rehan <rehanvladyslav@gmail.com>
Signed-off-by: Ivan Korneliuk <vansha@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>