VIM-92: Fix Vim keymap to work better in Mac OS

The problem is not completely solved. Please, review approach that I selected as a solution. 

In order to completely fix this I need Vim.xml generated by vim-plugin (with my changes) on Linux and Windows. Could you please attach it to this pull request (if it possible) or email me to alexander.zolotov@jetbrains.com? I want to compare it with old static Vim.xml. Most likely I will have to support custom shortcut-overrides for Linux and Windows default keymaps.