Add if/when clauses or similar to the keymap system

[danielzdev]

The current keymap context functionality in Zed offers powerful customization for when a keymap executes. However, I believe that adding "when" clauses (or more), similar to those found in VS Code, would significantly enhance this capability. For example, many keymaps currently lack a toggle function, requiring separate keybindings for opening and closing. With a "when" clause, I could simply use a single keymap to execute the close command if a specific panel, dock, or other element is already open, providing a more streamlined experience.

Something to the effect of:

{
  "context": "Editor"
  "bindings": {
    "space e": [
      { "command": "workspace::ToggleLeftDock", "when": "ProjectPanel && not_editing" },
      { "command": "project_panel::ToggleFocus", "when": "VimControl && !menu || EmptyPane" }
    ]
  }
}

In fact, I would go so far as to say I would prefer this over just being able to have a specific keymap that now toggles, versus just opening and closing, since there's more customization on the users part.