Add support for vscode-neovim

[searleser97]

Updated PR from: #284, just for reference

Context

1. vscode-neovim does not support conceal properly when highlighting for now, therefore, when using let g:sneak#label = 1 the labels were not shown as expected, instead, the first character of the match is shown always.
2. vscode-neovim supports text decorations to be shown on top of existing text with the option "vscode-neovim.textDecorationsAtTop": true in vscode's settings.json
3. easymotion plugin had a similar issue that was solved using textDecorations for vscode. See https://github.com/asvetliakov/vscode-neovim#vim-easymotion and commit adding text decorations

simplescreenrecorder-2021-10-07_12.18.10.mp4

note 1: all the labels have the same key on them
note 2: you can see the key strokes on the status line at the bottom

What does this PR do?

It adds support for vscode-neovim by adding text-decorations just when the user is in vscode

Evidence

simplescreenrecorder-2021-10-07_12.26.13.mp4

[theol0403]

Thanks for working on this! Is it totally necessary, though? About half a year ago, vim-sneak worked as-is in vscode-neovim, and then something broke - maybe a fix, rather than a completely different approach, would be better? What about adding support for the conceal property?

Imo, the easymotion text-decoration workaround isn't ideal either, it would be best to add extmark support to vscode-neovim and then use hop.nvim as-is.

[justinmk]

Besides the above question, #303 may also have helped here.

[searleser97]

Actually, Now there is no reason to keep using vim-sneak sine we now have leap plugin which works with VSCode and does better job than vim-sneak .

[justinmk]

Wrong. vim-sneak supports vim 7.3.