Update `Vim::activate` to ensure that the `Vim.focused` method is only
called if the associated editor is also focused.

This ensures that the `VimEvent::Focused` event is only emitted when the
editor is actually focused, preventing a bug where, after starting Zed,
Vim's mode indicator would show that the mode was `Insert` even though
it was in `Normal` mode in the main editor.

Closes #41353 

Release Notes:

- Fixed vim's mode being shown as `Inserted` right after opening Zed

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>