patch 8.2.1047: Vim9: script cannot use line continuation like :def function

Problem:    Vim9: script cannot use line continuation like in a :def function.
Solution:   Pass the getline function pointer to the eval() functions.  Use it
            for addition and multiplication operators.
diff --git a/src/list.c b/src/list.c
index 130ab25..c624003 100644
--- a/src/list.c
+++ b/src/list.c
@@ -1165,6 +1165,10 @@
     list_T	*l = NULL;
     typval_T	tv;
     listitem_T	*item;
+    evalarg_T	evalarg;
+
+    CLEAR_FIELD(evalarg);
+    evalarg.eval_flags = flags;
 
     if (evaluate)
     {
@@ -1176,7 +1180,7 @@
     *arg = skipwhite(*arg + 1);
     while (**arg != ']' && **arg != NUL)
     {
-	if (eval1(arg, &tv, flags) == FAIL)	// recursive!
+	if (eval1(arg, &tv, &evalarg) == FAIL)	// recursive!
 	    goto failret;
 	if (evaluate)
 	{