patch 8.1.1905: cannot set all properties of the info popup

Problem:    Cannot set all properties of the info popup.
Solution:   Add popup_findinfo().  Rename popup_getpreview() to
            popup_findpreview().
diff --git a/runtime/doc/popup.txt b/runtime/doc/popup.txt
index 67ad70b..e766deb 100644
--- a/runtime/doc/popup.txt
+++ b/runtime/doc/popup.txt
@@ -289,6 +289,20 @@
 		See the example here: |popup_dialog-example|
 
 
+popup_findinfo()					*popup_findinfo()*
+		Get the |window-ID| for the popup info window, as it used by
+		the popup menu.  See |complete-popup|.  The info popup is
+		hidden when not used, it can be deleted with |popup_clear()|
+		and |popup_close()|.
+		Return zero if there is none.
+
+
+popup_findpreview()					*popup_findpreview()*
+		Get the |window-ID| for the popup preview window.
+		Return zero if there is none.
+
+
+
 popup_getoptions({id})					*popup_getoptions()*
 		Return the {options} for popup {id} in a Dict.
 		A zero value means the option was not set.  For "zindex" the
@@ -336,10 +350,6 @@
 
 		If popup window {id} is not found an empty Dict is returned.
 
-popup_getpreview()					*popup_getpreview()*
-		Get the |window-ID| for the popup preview window.
-		Return zero if there is none.
-
 
 popup_hide({id})						*popup_hide()*
 		If {id} is a displayed popup, hide it now. If the popup has a