patch 8.1.1410: popup_move() is not implemented yet

Problem:    Popup_move() is not implemented yet.
Solution:   Implement it. (Yasuhiro Matsumoto, closes #4441)  Improve the
            positioning and resizing.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index b15e74d..03e3260 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -811,6 +811,7 @@
     {"popup_close",	1, 1, f_popup_close},
     {"popup_create",	2, 2, f_popup_create},
     {"popup_hide",	1, 1, f_popup_hide},
+    {"popup_move",	2, 2, f_popup_move},
     {"popup_show",	1, 1, f_popup_show},
 #endif
 #ifdef FEAT_FLOAT