Migrate MR merged/closed time tooltip to GitLab UI

app/assets/javascripts/vue_merge_request_widget/components/mr_widget_author_time.vue

 <script>
-import tooltip from '~/vue_shared/directives/tooltip';
+import { GlTooltipDirective } from '@gitlab/ui';
 import MrWidgetAuthor from './mr_widget_author.vue';
 
 export default {
@@ -8,7 +8,7 @@ export default {
     MrWidgetAuthor,
   },
   directives: {
-    tooltip,
+    GlTooltip: GlTooltipDirective,
   },
   props: {
     actionText: {
@@ -34,6 +34,7 @@ export default {
   <h4 class="js-mr-widget-author">
     {{ actionText }}
     <mr-widget-author :author="author" />
-    <time v-tooltip :title="dateTitle" data-container="body"> {{ dateReadable }} </time>
+    <span class="sr-only">{{ dateReadable }} ({{ dateTitle }})</span>
+    <time v-gl-tooltip.hover aria-hidden :title="dateTitle"> {{ dateReadable }} </time>
   </h4>
 </template>

spec/frontend/vue_mr_widget/components/mr_widget_author_time_spec.js

@@ -35,9 +35,7 @@ describe('MrWidgetAuthorTime', () => {
   });
 
   it('renders provided time', () => {
-    expect(vm.$el.querySelector('time').getAttribute('data-original-title')).toEqual(
-      '2017-03-23T23:02:00.807Z',
-    );
+    expect(vm.$el.querySelector('time').getAttribute('title')).toEqual('2017-03-23T23:02:00.807Z');
 
     expect(vm.$el.querySelector('time').textContent.trim()).toEqual('12 hours ago');
   });

spec/frontend/vue_mr_widget/components/states/mr_widget_merged_spec.js

@@ -212,8 +212,6 @@ describe('MRWidgetMerged', () => {
   });
 
   it('should use mergedEvent mergedAt as tooltip title', () => {
-    expect(vm.$el.querySelector('time').getAttribute('data-original-title')).toBe(
-      'Jan 24, 2018 1:02pm GMT+0000',
-    );
+    expect(vm.$el.querySelector('time').getAttribute('title')).toBe('Jan 24, 2018 1:02pm GMT+0000');
   });
 });