patch 9.1.0068: Visual highlighting can still be improved

Problem:  Visual highlighting can still be improved
Solution: Update Visual highlighting for 8 color terminals,
          use uniform grey highlighting for dark and light bg
          (Maxim Kim)

Update terminal Visual

1. Use `ctermbg=Grey ctermfg=Black` for both dark and light

This uniforms Visual highlighting between default dark and light colors
And should work for vim usually detecting light background for terminals
with black/dark background colors.

Previously used `ctermfg=White` leaks `cterm=bold` if available colors
are less than 16.

2. Use `term=reverse cterm=reverse ctermbg=NONE ctermfg=NONE`
   for terminals reporting less than 8 colors available

If the terminal has less than 8 colors, grey just doesn't work right

closes: #13940

Signed-off-by: Maxim Kim <habamax@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    68,
 /**/
     67,
 /**/