vim: Maintain block cursor for navigating/non-modifying operators (#21502)

The cursor shape now only changes to underline for operators that modify
text (like: delete, change, yank) while maintaining block shape for
navigation operators (like: find, till).

This better matches Vim/Nvim's behavior where the cursor only changes
shape when an operator that will modify text is pending.

Release Notes:

- vim: Improved cursor shape behavior to better match Vim