cinnamonEntry.js: Allow addContextMenu() to re-use an existing

PopupMenuManager.

If the St.Entry is inside of a popup menu (and *not* a modal dialog),
that menu's 'captured-event' handler can receive unintended events,
and react to focus loss, closing both the original popup and context
menu.

The original menu's manager can safely deal with multiple popups,
and ensure 'correct' behavior in this situation.

ref:
#13472

Author: mtwebster

js/ui/cinnamonEntry.js

@@ -139,13 +139,30 @@ function _onPopup(actor) {
     entry._menu.open();
 };
 
-function addContextMenu(entry, params) {
+/**
+ * addContextMenu:
+ * @entry (St.Entry): the entry to add a context menu to
+ * @params (object): optional parameters to pass to the _EntryMenu constructor.
+ *   Currently supports `isPassword` (boolean) to add a show/hide text toggle.
+ * @parentMenu (PopupMenu.PopupMenu): optional parent menu. When the entry is
+ *   inside an existing popup menu (e.g. an applet menu), pass the parent menu
+ *   here so the context menu is registered as a child menu. This prevents the
+ *   parent menu from closing when the context menu is interacted with. When
+ *   omitted, a standalone PopupMenuManager is created for the context menu,
+ *   which is appropriate for entries in dialogs or other non-menu contexts.
+ */
+function addContextMenu(entry, params, parentMenu) {
     if (entry._menu)
         return;
 
     entry._menu = new _EntryMenu(entry, params);
-    entry._menuManager = new PopupMenu.PopupMenuManager({ actor: entry });
-    entry._menuManager.addMenu(entry._menu);
+
+    if (parentMenu) {
+        parentMenu.addChildMenu(entry._menu);
+    } else {
+        entry._menuManager = new PopupMenu.PopupMenuManager({ actor: entry });
+        entry._menuManager.addMenu(entry._menu);
+    }
 
     // Add a click action to both the entry and its clutter_text; the former
     // so padding is included in the clickable area, the latter because the