Add "leave-current-mode" command to move insert->normal->command.

[asford]

As we know, jupyterlab is already a "modal" editor and (by default) has a "edit4" and "command" mode.
One switches between modes via Esc, a la vim.

It's rather nice to preserve this behavior when adding the vim-modes so that Esc conceptually moves "up" a mode,
from vim-insert/lvisual to vim-normal and from vim-normal to jupyterlab-command.

Add a "Leave Current Mode" command, which can be rebound to Esc rather than "Leave Insert Mode".

This PR does not change the default Esc binding, which is separately proposed in #70.

Please finish the following when submitting a pull request:

• Add a line to History.md briefly documenting the change.

If this is a release, additionally do the following:

• Update the dependencies in package.json
• Run jlpm install to update yarn.lock

Thanks!

[github-actions]

👈 Launch a binder notebook on branch asford/jupyterlab-vim/leave_current_mode

[ianhi]

Sorry I missed this @asford - this is a nice addition!

a few comments on the code if you have the time to address but otherwise looks good.

I also kind of like having equivalent behavior available for i - so i can take you from jupyter command mode -> normal mode -> edit mode. What do you think about that?

[peytondmurray]

Hmm, I was just testing this out but was unable to find the leave-current-mode option in the Keyboard Shortcuts section of the Advanced Settings Editor. I did a pip install . inside the base of this repo on this branch. What am I missing? I can see leave-insert-mode...

EDIT: Okay, I think I might not be able to see this because it's not part of plugin.json, even though it's been added to the command registry. Please disregard the comment above.