GtkFileChooserWidget: Propagate keys from external entry to fcwidget at the BUBBLE phase

Now that we use event controllers we can forward keybindings from the
external entry to the filechooserwidget at the bubble phase.

Fixes #4905

 * commit 1fb075db
 * commit 686116ba
12 jobs for file-chooser-widget-make-key-controller-on-external-entry-work-at-bubble-phase in 14 minutes and 21 seconds (queued for 2 minutes and 36 seconds)