Use dynamic filter expansion for plugin filters

Plugin-registered filter fields are not rendered with the dynamic
expansion feature, even though it is supported.

Added the class to the link tag to enable the script on plugin filter
fields.

Fixes #20481

Signed-off-by: Damien Regad <dregad@mantisbt.org>

core/filter_api.php

@@ -3053,7 +3053,7 @@ function filter_draw_selection_area2( $p_page_number, $p_for_screen = true, $p_e
 			}
 			$t_colspan_attr = ( $t_colspan > 1 ? 'colspan="' . $t_colspan . '" ' : '' );
 			$t_plugin_filter_links[$t_assigned_row][] = '<td ' . $t_colspan_attr . 'class="small-caption"> <a href="' . $t_filters_url . string_attribute( $t_field_name ) .
-				'" id="' . string_attribute( $t_field_name ) . '_filter">' . string_display_line( $t_filter_object->title ) . '</a> </td>';
+				'" id="' . string_attribute( $t_field_name ) . '_filter"' . $t_dynamic_filter_expander_class . '>' . string_display_line( $t_filter_object->title ) . '</a> </td>';
 			$t_values = '<td ' . $t_colspan_attr . 'class="small-caption" id="' . string_attribute( $t_field_name ) . '_filter_target"> ';
 
 			if( !isset( $t_filter[$t_field_name] ) ) {