dbusServices/screencast: Check for all require elements

Instead of assuming that gst-plugins-good has been compiled with
all the plugins we need enabled, explicitly check for the ones
we use.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5710

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2519>

js/dbusServices/screencast/screencastService.js

@@ -259,9 +259,13 @@ var Recorder = class {
 
 var ScreencastService = class extends ServiceImplementation {
     static canScreencast() {
+        const elements = [
+            'pipewiresrc',
+            'filesink',
+            ...DEFAULT_PIPELINE.split('!').map(e => e.trim().split(' ').at(0)),
+        ];
         return Gst.init_check(null) &&
-            Gst.ElementFactory.find('pipewiresrc') &&
-            Gst.ElementFactory.find('filesink');
+            elements.every(e => Gst.ElementFactory.find(e) != null);
     }
 
     constructor() {