MDL-77105 mod_lti: Add 'nofilter' class for custom tool icons

Add a '.nofilter' class when rendering custom tool icons in order
to render them as is and without CSS filter on the activity chooser.

mod/lti/locallib.php

@@ -2323,7 +2323,15 @@ function lti_get_configured_types($courseid, $sectionreturn = 0) {
             $type->help     = clean_param($trimmeddescription, PARAM_NOTAGS);
             $type->helplink = get_string('modulename_shortcut_link', 'lti');
         }
-        $type->icon = html_writer::empty_tag('img', ['src' => get_tool_type_icon_url($ltitype), 'alt' => '', 'class' => 'icon']);
+
+        $iconurl = get_tool_type_icon_url($ltitype);
+        $iconclass = '';
+        if ($iconurl !== $OUTPUT->image_url('monologo', 'lti')->out()) {
+            // Do not filter the icon if it is not the default LTI activity icon.
+            $iconclass = 'nofilter';
+        }
+        $type->icon = html_writer::empty_tag('img', ['src' => $iconurl, 'alt' => '', 'class' => "icon $iconclass"]);
+
         $type->link = new moodle_url('/course/modedit.php', array('add' => 'lti', 'return' => 0, 'course' => $courseid,
             'sr' => $sectionreturn, 'typeid' => $ltitype->id));
         $types[] = $type;