Ever since we launched the keymap editor, we've received feedback about
how "_creating_" a new keybinding was not obvious. At first, I was
confused about this feedback because you can't "create" a keybinding,
you need to rather _assign it_ to an action... so what always made sense
to me was to start with searching for the action, which is an use case
we already support. Regardless, having an easy to reach "create" button,
which essentially still asks for action > keystroke > arguments (if
needed) > and context, feels like a win UX-wise; a bit of a redundant
flow that feels ultimately positive.

So, this PR adds a "Create Keybinding" button to the keymap editor,
which you can reach with `cmd-k`. That will open up a modal with an
action autocomplete, the keystroke recording input, the arguments input
(if needed), and the context input.


https://github.com/user-attachments/assets/86f64314-4685-47bb-bb0d-72ca4c469d1f

Release Notes:

- keymap editor: Added a keybinding creation modal to make it easier to
assign an action to a keystroke.