patch 8.1.1978: the eval.c file is too big

Problem:    The eval.c file is too big.
Solution:   Move filter() and map() to list.c.
diff --git a/src/proto/list.pro b/src/proto/list.pro
index 3102bb2..7a1ce7a 100644
--- a/src/proto/list.pro
+++ b/src/proto/list.pro
@@ -41,4 +41,6 @@
 void list_remove(typval_T *argvars, typval_T *rettv, char_u *arg_errmsg);
 void f_sort(typval_T *argvars, typval_T *rettv);
 void f_uniq(typval_T *argvars, typval_T *rettv);
+void f_filter(typval_T *argvars, typval_T *rettv);
+void f_map(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */