vim: Fix cw with count greater than 1 not preserving whitespace correctly

[davidhi7]

In vim, c {count} w diverges from the default w motion behavior: For change operations, the w motion will be treated like the e motion if the cursor is on a word, preserving whitespace after the N-th word. In zed, this special case was only implemented for a count of 1, falling back to incorrectly using the w motion if the count is greater than 1.

This PR generalizes this implementation to handle this special case for any count.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Closes #56563.

Release Notes:

• Fixed: vim cw with count greater than 1 not preserving whitespace correctly