patch 9.0.1292: :defer may call the wrong method for an object

Problem:    :defer may call the wrong method for an object. (Ernie Rael)
Solution:   When en object is from a class that extends or implements, figure
            out the method to call at runtime. (closes #11910)
diff --git a/src/vim9.h b/src/vim9.h
index fd98bb5..4df97c6 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -380,6 +380,8 @@
 typedef struct {
     char_u	  *fre_func_name;	// function name for legacy function
     loopvarinfo_T fre_loopvar_info;	// info about variables inside loops
+    class_T	  *fre_class;		// class for a method
+    int		  fre_method_idx;	// method index on "fre_class"
 } funcref_extra_T;
 
 // arguments to ISN_FUNCREF