patch 9.0.0481: in :def function all closures in loop get the same variables

Problem:    In a :def function all closures in a loop get the same variables.
Solution:   Use a separate list of variables for LOADOUTER and STOREOUTER.
            Not copied at end of loop yet.

src/vim9.h

@@ -354,16 +354,29 @@ typedef struct {
     int		ul_forceit;	// forceit flag
 } unlet_T;
 
+// extra arguments for funcref_T
+typedef struct {
+    char_u	*fre_func_name;	    // function name for legacy function
+    short	fre_loop_var_idx;   // index of first variable inside loop
+    short	fre_loop_var_count; // number of variables inside loop
+} funcref_extra_T;
+
 // arguments to ISN_FUNCREF
 typedef struct {
-    int		fr_dfunc_idx;	// function index for :def function
-    char_u	*fr_func_name;	// function name for legacy function
+    int		    fr_dfunc_idx;   // function index for :def function
+    funcref_extra_T *fr_extra;	    // optional extra information
 } funcref_T;
 
 // arguments to ISN_NEWFUNC
 typedef struct {
-    char_u	*nf_lambda;	// name of the lambda already defined
-    char_u	*nf_global;	// name of the global function to be created
+    char_u	*nfa_lambda;	   // name of the lambda already defined
+    char_u	*nfa_global;	   // name of the global function to be created
+    short	nfa_loop_var_idx;    // index of first variable inside loop
+    short	nfa_loop_var_count;  // number of variables inside loop
+} newfuncarg_T;
+
+typedef struct {
+    newfuncarg_T *nf_arg;
 } newfunc_T;
 
 // arguments to ISN_CHECKLEN
@@ -401,6 +414,8 @@ typedef struct {
     int		outer_depth;	// nesting level, stack frames to go up
 } isn_outer_T;
 
+#define OUTER_LOOP_DEPTH -9	// used for outer_depth for loop variables
+
 // arguments to ISN_SUBSTITUTE
 typedef struct {
     char_u	*subs_cmd;	// :s command
@@ -677,6 +692,7 @@ typedef struct {
     char_u	*lv_name;
     type_T	*lv_type;
     int		lv_idx;		// index of the variable on the stack
+    int		lv_loop_idx;	// index of first variable inside a loop or -1
     int		lv_from_outer;	// nesting level, using ctx_outer scope
     int		lv_const;	// when TRUE cannot be assigned to
     int		lv_arg;		// when TRUE this is an argument