Add model preview to upload page

Signed-off-by: Justin Georgi <justin.georgi@gmail.com>

includes/GlModelHooks.php

@@ -2,6 +2,7 @@
 namespace MediaWiki\Extension\GlModelViewer;
 
 use MediaWiki\MediaWikiServices;
+use RequestContext;
 use Html;
 use ParserOutput;
 
@@ -100,6 +101,22 @@ class GlModelHooks {
         return false;
     }
 
+    /**
+     * MWHook: Occurs after the descriptor for the upload form as been assembled.
+     * 
+     * @param $descriptor the HTMLForm descriptor
+     */
+    public static function onUploadFormInitDescriptor( $descriptor ) {
+        $context = RequestContext::getMain();
+        $out = $context->getOutput();
+        $mvScriptAttr = array(
+            'src' => 'https://ajax.googleapis.com/ajax/libs/model-viewer/3.5.0/model-viewer.min.js',
+            'type' => 'module'
+            );
+        $out->addHeadItems(Html::rawElement('script',$mvScriptAttr));
+        $out->addModules('ext.glmv.upl');
+    }
+
     /**
      * Small helper function to display information on the browser console
      *