patch 8.2.0600: Vim9: cannot read or write w:, t: and b: variables

Problem:    Vim9: cannot read or write w:, t: and b: variables.
Solution:   Implement load and store for w:, t: and b: variables.
            (closes #5950)

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    600,
 /**/
     599,
 /**/