patch 8.2.1329: Vim9: cannot define global function inside :def function

Problem:    Vim9: cannot define global function inside :def function.
Solution:   Assign to global variable instead of local. (closes #6584)

src/vim9.h

@@ -79,6 +79,7 @@ typedef enum {
     ISN_PCALL_END,  // cleanup after ISN_PCALL with cpf_top set
     ISN_RETURN,	    // return, result is on top of stack
     ISN_FUNCREF,    // push a function ref to dfunc isn_arg.funcref
+    ISN_NEWFUNC,    // create a global function from a lambda function
 
     // expression operations
     ISN_JUMP,	    // jump if condition is matched isn_arg.jump
@@ -237,6 +238,12 @@ typedef struct {
     int		fr_var_idx;	// variable to store partial
 } 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
+} newfunc_T;
+
 // arguments to ISN_CHECKLEN
 typedef struct {
     int		cl_min_len;	// minimum length
@@ -281,6 +288,7 @@ struct isn_S {
 	script_T	    script;
 	unlet_T		    unlet;
 	funcref_T	    funcref;
+	newfunc_T	    newfunc;
 	checklen_T	    checklen;
 	shuffle_T	    shuffle;
     } isn_arg;