Unable to remap <C-s> in insert mode

[alexriedl]

Is this a BUG REPORT or FEATURE REQUEST? (choose one): Bug Report

What happened:
Mapped <C-s> using vim.insertModeKeyBindingsNonRecursive and was unable to the mapped commands to happen. Mapped <C-n> to the same commands and that worked.

What did you expect to happen:
While in insert mode I should be able to press <C-s> or <C-n> to save the file and exit insert mode.

How to reproduce it (as minimally and precisely as possible):

1. Add to your user settings:

"vim.insertModeKeyBindingsNonRecursive": [
    {
        "before": [ "<C-s>" ],
        "commands": [
            { "command": "workbench.action.files.save" },
            { "command": "extension.vim_escape" }
        ]
    },
    {
        "before": [ "<C-n>" ],
        "commands": [
            { "command": "workbench.action.files.save" },
            { "command": "extension.vim_escape" }
        ]
    }
],

2. Reload window
3. Open a file and enter insert mode (make a change)
4. Hit <C-s>, nothing will happen. Hit <C-n> File will be saved and you will be taken out of insert mode.

Environment:

• Extension (VsCodeVim) version: 0.11.0
• VSCode version: 1.20.1
• OS version: Ubuntu 17.10

[AntonPuko]

The same issue with <C-;> in insert mode.

  "vim.handleKeys": {
    "<C-;>": true,
  }
...
  "vim.insertModeKeyBindings": [
    {
      "before": [
        "<C-;>",
      ],
      "after": [
        "<right>",
      ]
    }
  ]

it works with <C-n>

[jpoon]

Our extension doesn't bind to those keys (https://github.com/VSCodeVim/Vim/blob/master/package.json#L140), hence they go straight to the editor and vscodevim has no history of it.

If we do bind to them, that means we'll need to handle whatever <c-n> and <c-s> they are supposed to do in the editor (ie. new window/save) in the event that there is no user remapping for those keys.

[jpoon]

Dupe of #757