Add Expand/Collapse screenreader message on Modules

Fixes CNVS-20464

Test Plan:
- Use NVDA on Firefox and navigate to Modules page
- Expand and collapse a module
- You should expect to hear "Exapnded" and "Collaped"
  from the screenreader

Change-Id: I29778f8c26d1d9e54c1e4ef40c96dec107521232
Reviewed-on: https://gerrit.instructure.com/57615
Tested-by: Jenkins
Reviewed-by: Sterling Cobb <sterling@instructure.com>
QA-Review: Adam Stone <astone@instructure.com>
Product-Review: Brock Cooper <bcooper@instructure.com>

public/javascripts/context_modules.js

@@ -45,7 +45,8 @@ define([
   'jquery.templateData' /* fillTemplateData, getTemplateData */,
   'vendor/date' /* Date.parse */,
   'vendor/jquery.scrollTo' /* /\.scrollTo/ */,
-  'jqueryui/sortable' /* /\.sortable/ */
+  'jqueryui/sortable' /* /\.sortable/ */,
+  'compiled/jquery.rails_flash_notifications'
 ], function(_, ModuleFile, PublishCloud, React, PublishableModuleItem, PublishIconView, INST, I18n, $, ContextModulesView, RelockModulesDialog, vddTooltip, vddTooltipView, Publishable, PublishButtonView, htmlEscape) {
 
   // TODO: AMD don't export global, use as module
@@ -1598,12 +1599,14 @@ define([
             $module.toggleClass('collapsed_module', false);
             // Makes sure the resulting item has focus.
             $module.find(".collapse_module_link").focus();
+            $.screenReaderFlashMessage(I18n.t('Expanded'));
             
           } else {
             $module.find(".footer .manage_module").css('display', ''); //'none');
             $module.toggleClass('collapsed_module', true);
             // Makes sure the resulting item has focus.
             $module.find(".expand_module_link").focus();
+            $.screenReaderFlashMessage(I18n.t('Collapsed'));
           }
           if(expandCallback && $.isFunction(expandCallback)) {
             expandCallback();