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/ex_eval.c b/src/ex_eval.c
index a13f844..cb32bd0 100644
--- a/src/ex_eval.c
+++ b/src/ex_eval.c
@@ -895,9 +895,12 @@
 ex_eval(exarg_T *eap)
 {
     typval_T	tv;
+    evalarg_T	evalarg;
 
-    if (eval0(eap->arg, &tv, &eap->nextcmd, eap->skip ? 0 : EVAL_EVALUATE)
-									 == OK)
+    evalarg.eval_flags = eap->skip ? 0 : EVAL_EVALUATE;
+    evalarg.eval_cookie = eap->getline == getsourceline ? eap->cookie : NULL;
+
+    if (eval0(eap->arg, &tv, &eap->nextcmd, &evalarg) == OK)
 	clear_tv(&tv);
 }