patch 8.2.0818: Vim9: using a discovery phase doesn't work well

Problem:    Vim9: using a discovery phase doesn't work well.
Solution:   Remove the discovery phase, instead compile a function only when
            it is used.  Add :defcompile to compile def functions earlier.

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    818,
 /**/
     817,
 /**/