Migrate revert and cherry-pick MR tooltips

Migrate tooltips of those two buttons to GitLab UI

app/assets/javascripts/vue_merge_request_widget/components/states/mr_widget_merged.vue

 <script>
 /* eslint-disable @gitlab/vue-require-i18n-strings */
-import { GlLoadingIcon, GlButton } from '@gitlab/ui';
+import { GlLoadingIcon, GlButton, GlTooltipDirective } from '@gitlab/ui';
 import { deprecatedCreateFlash as Flash } from '~/flash';
-import tooltip from '~/vue_shared/directives/tooltip';
 import { s__, __ } from '~/locale';
 import ClipboardButton from '~/vue_shared/components/clipboard_button.vue';
 import MrWidgetAuthorTime from '../mr_widget_author_time.vue';
@@ -12,7 +11,7 @@ import eventHub from '../../event_hub';
 export default {
   name: 'MRWidgetMerged',
   directives: {
-    tooltip,
+    GlTooltip: GlTooltipDirective,
   },
   components: {
     MrWidgetAuthorTime,
@@ -115,7 +114,7 @@ export default {
         />
         <gl-button
           v-if="mr.canRevertInCurrentMR"
-          v-tooltip
+          v-gl-tooltip.hover
           :title="revertTitle"
           size="small"
           category="secondary"
@@ -128,7 +127,7 @@ export default {
         </gl-button>
         <gl-button
           v-else-if="mr.revertInForkPath"
-          v-tooltip
+          v-gl-tooltip.hover
           :href="mr.revertInForkPath"
           :title="revertTitle"
           size="small"
@@ -140,7 +139,7 @@ export default {
         </gl-button>
         <gl-button
           v-if="mr.canCherryPickInCurrentMR"
-          v-tooltip
+          v-gl-tooltip.hover
           :title="cherryPickTitle"
           size="small"
           href="#modal-cherry-pick-commit"
@@ -151,7 +150,7 @@ export default {
         </gl-button>
         <gl-button
           v-else-if="mr.cherryPickInForkPath"
-          v-tooltip
+          v-gl-tooltip.hover
           :href="mr.cherryPickInForkPath"
           :title="cherryPickTitle"
           size="small"