* Update `Vim::register` to correctly re-activate when either `vim_mode`
  or `helix_mode` are enabled, when they were previously disabled.
* Update `settings_ui::page_data::keymap_page` such that, when enabling
  or disabling `vim_mode` or `helix_mode`, the other setting is
  disabled, in case it is set. This ensures that only one mode is
  enabled at a time, as it should be.
  
Closes #51704 

Release Notes:

- Fixed switching between vim and helix mode needing multiple calls to
  have an effect while an editor is already open
- Update Settings UI such that, enabling vim or helix mode, now disables
  the other if it was previously active

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Co-authored-by: dino <dinojoaocosta@gmail.com>