Focus the project manager's search box automatically on startup

This allows the user to search projects as soon as the project manager
opens, without having to click on the search field first.

editor/project_manager.cpp

@@ -1757,6 +1757,12 @@ void ProjectManager::_notification(int p_what) {
 
 			if (_project_list->get_project_count() == 0 && StreamPeerSSL::is_available())
 				open_templates->popup_centered_minsize();
+
+			if (_project_list->get_project_count() >= 1) {
+				// Focus on the search box immediately to allow the user
+				// to search without having to reach for their mouse
+				project_filter->search_box->grab_focus();
+			}
 		} break;
 		case NOTIFICATION_VISIBILITY_CHANGED: {