patch 8.2.4137: Vim9: calling import with and without method is inconsistent

Problem:    Vim9: calling import with and without method is inconsistent.
Solution:   Set a flag that a parenthsis follows to compile_load_scriptvar().
            Add some more tests.  Improve error message.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4137,
 /**/
     4136,
 /**/