Themes: Fix themes search event not firing on enter.

Attach the submit event to the parent search form in the installed and add new theme screen. Following [58405], the submit event was no longer attached to an object that was able to handle form submissions.

Props nithi22, nithins53, josklever, the-ank, debarghyabanerjee, sabernhardt, jeherve, hellofromtonya.
Fixes #61578.

git-svn-id: https://develop.svn.wordpress.org/trunk@58914 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/js/_enqueues/wp/theme.js

@@ -96,7 +96,7 @@ themes.view.Appearance = wp.Backbone.View.extend({
 	},
 
 	// Defines search element container.
-	searchContainer: $( '.search-form .search-box' ),
+	searchContainer: $( '.search-form' ),
 
 	// Search input and view
 	// for current theme collection.
@@ -118,11 +118,13 @@ themes.view.Appearance = wp.Backbone.View.extend({
 		// Render and append after screen title.
 		view.render();
 		this.searchContainer
+			.find( '.search-box' )
 			.append( $.parseHTML( '<label for="wp-filter-search-input">' + l10n.search + '</label>' ) )
-			.append( view.el )
-			.on( 'submit', function( event ) {
-				event.preventDefault();
-			});
+			.append( view.el );
+
+		this.searchContainer.on( 'submit', function( event ) {
+			event.preventDefault();
+		});
 	},
 
 	// Checks when the user gets close to the bottom