patch 8.2.4053: Vim9: autoload mechanism doesn't fully work yet

Problem:    Vim9: autoload mechanism doesn't fully work yet.
Solution:   Define functions and variables with their autoload name, add the
            prefix when calling a function, find the variable in the table of
            script variables.
diff --git a/src/proto/scriptfile.pro b/src/proto/scriptfile.pro
index 140d67b..477dc3e 100644
--- a/src/proto/scriptfile.pro
+++ b/src/proto/scriptfile.pro
@@ -38,6 +38,7 @@
 void do_finish(exarg_T *eap, int reanimate);
 int source_finished(char_u *(*fgetline)(int, void *, int, getline_opt_T), void *cookie);
 char_u *script_name_after_autoload(scriptitem_T *si);
+char_u *get_autoload_prefix(scriptitem_T *si);
 char_u *may_prefix_autoload(char_u *name);
 char_u *autoload_name(char_u *name);
 int script_autoload(char_u *name, int reload);