patch 8.2.1349: Vim9: can define a function with the name of an import

Problem:    Vim9: can define a function with the name of an import.
Solution:   Disallow using an existing name. (closes #6585)
diff --git a/src/globals.h b/src/globals.h
index a0ebc45..cc01ac2 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1746,6 +1746,7 @@
 EXTERN char e_duplicate_key[]	INIT(= N_("E721: Duplicate key in Dictionary: \"%s\""));
 EXTERN char e_missing_dict_comma[] INIT(= N_("E722: Missing comma in Dictionary: %s"));
 EXTERN char e_missing_dict_end[]    INIT(= N_("E723: Missing end of Dictionary '}': %s"));
+EXTERN char e_already_defined[] INIT(= N_("E1073: name already defined: %s"));
 #endif
 #ifdef FEAT_CLIENTSERVER
 EXTERN char e_invexprmsg[]	INIT(= N_("E449: Invalid expression received"));