Add an implementation of junegunn/vim-peekaboo plugin

[harri-halttunen-aktia]

Is your feature request related to a problem? Please describe. It would be nice to quickly see the content of registers in a popup when user presses ", @ or Ctrl+R.

Describe the solution you'd like The similar approach than junegunn/vim-peekaboo but by means that suit VSCode.

Describe alternatives you've considered None (except neovim, of course).

Additional context See junegunn/vim-peekaboo for further details.