patch 8.2.4140: maparg() does not indicate the type of script

Problem:    maparg() does not indicate the type of script where it was defined.
Solution:   Add "scriptversion".
diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 3850b38..403f592 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -5247,6 +5247,8 @@
 				     (|mapmode-ic|)
 		  "sid"	     The script local ID, used for <sid> mappings
 			     (|<SID>|).
+		  "scriptversion"  The version of the script.  999999 for
+		  		   |Vim9| script.
 		  "lnum"     The line number in "sid", zero if unknown.
 		  "nowait"   Do not wait for other, longer mappings.
 			     (|:map-<nowait>|).