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.
diff --git a/src/proto/userfunc.pro b/src/proto/userfunc.pro
index 4295ce2..6ed79ba 100644
--- a/src/proto/userfunc.pro
+++ b/src/proto/userfunc.pro
@@ -23,8 +23,9 @@
 int call_func(char_u *funcname, int len, typval_T *rettv, int argcount_in, typval_T *argvars_in, funcexe_T *funcexe);
 char_u *trans_function_name(char_u **pp, int *is_global, int skip, int flags, funcdict_T *fdp, partial_T **partial);
 char_u *untrans_function_name(char_u *name);
-ufunc_T *def_function(exarg_T *eap, char_u *name_arg, void *context, int compile);
+ufunc_T *def_function(exarg_T *eap, char_u *name_arg);
 void ex_function(exarg_T *eap);
+void ex_defcompile(exarg_T *eap);
 int eval_fname_script(char_u *p);
 int translated_function_exists(char_u *name, int is_global);
 int has_varargs(ufunc_T *ufunc);