Decide whether to highlight the visual-selected character under the
cursor, depending on 'guicursor' style:
- Highlight if cursor is blinking or non-block (vertical, horiz).
- Do NOT highlight if cursor is non-blinking block.
Traditionally Vim's visual selection does "reverse mode", which perhaps
conflicts with the non-blinking block cursor. But 'guicursor' defaults
to a vertical bar for selection=exclusive, and this confuses users who
expect to see the text highlighted.
closes#8983
37a499148f