patch 8.2.4683: verbose check with dict_find() to see if a key is present

Problem:    Verbose check with dict_find() to see if a key is present.
Solution:   Add dict_has_key(). (Yegappan Lakshmanan, closes #10074)
diff --git a/src/popupwin.c b/src/popupwin.c
index c3251ea..9c0cade 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -1957,7 +1957,7 @@
 
     if (d != NULL)
     {
-	if (dict_find(d, (char_u *)"tabpage", -1) != NULL)
+	if (dict_has_key(d, "tabpage"))
 	    tabnr = (int)dict_get_number(d, (char_u *)"tabpage");
 	else if (type == TYPE_NOTIFICATION)
 	    tabnr = -1;  // notifications are global by default