st/entry: Bind ClutterText reactivity to entry

The text is part of the entry, so it is surprising that it can
still be edited when the entry itself isn't reactive. Address
this by setting up a binding instead of expecting all consumers
to handle the case themselves.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/2423

js/ui/appDisplay.js

@@ -691,7 +691,6 @@ var AllView = GObject.registerClass({
 
             // Toggle search entry
             Main.overview.searchEntry.reactive = !isOpen;
-            Main.overview.searchEntry.clutter_text.reactive = !isOpen;
             Main.overview.searchEntry.clutter_text.editable = !isOpen;
 
             this._displayingPopup = isOpen;

src/st/st-entry.c

@@ -977,6 +977,10 @@ st_entry_init (StEntry *entry)
                               "single-line-mode", TRUE,
                               NULL);
 
+  g_object_bind_property (G_OBJECT (entry), "reactive",
+                          priv->entry, "reactive",
+                          G_BINDING_DEFAULT);
+
   g_signal_connect (priv->entry, "key-focus-in",
                     G_CALLBACK (clutter_text_focus_in_cb), entry);