Flash is now a ES6 module

Reduced the technical debt around our JS flash function by making it a
module that is imported rather than relying on the global function.
The global function still exists mainly for technical debt with how
some requests are being completed, but new JS should import the module
directly.

Also reduces some tech debt in the file by removing the need for jQuery.
Instead Flash is now 100% vanilla JS.

app/assets/javascripts/notes/components/issue_notes_app.vue

 <script>
-  /* global Flash */
   import { mapGetters, mapActions } from 'vuex';
+  import Flash from '../../flash';
   import store from '../stores/';
   import * as constants from '../constants';
   import issueNote from './issue_note.vue';

app/assets/javascripts/notes/stores/actions.js

-/* global Flash */
 import Visibility from 'visibilityjs';
+import Flash from '../../flash';
 import Poll from '../../lib/utils/poll';
 import * as types from './mutation_types';
 import * as utils from './utils';
@@ -99,7 +99,7 @@ export const saveNote = ({ commit, dispatch }, noteData) => {
         eTagPoll.makeRequest();
         $('.js-gfm-input').trigger('clear-commands-cache.atwho');
-        Flash('Commands applied', 'notice', $(noteData.flashContainer));
+        Flash('Commands applied', 'notice', noteData.flashContainer);
       }
       if (commandsChanges) {
@@ -114,8 +114,8 @@ export const saveNote = ({ commit, dispatch }, noteData) => {
             .catch(() => {
               Flash(
                 'Something went wrong while adding your award. Please try again.',
-                null,
-                $(noteData.flashContainer),
+                'alert',
+                noteData.flashContainer,
               );
             });
         }
@@ -126,7 +126,7 @@ export const saveNote = ({ commit, dispatch }, noteData) => {
       }
       if (errors && errors.commands_only) {
-        Flash(errors.commands_only, 'notice', $(noteData.flashContainer));
+        Flash(errors.commands_only, 'notice', noteData.flashContainer);
       }
       commit(types.REMOVE_PLACEHOLDER_NOTES);

app/assets/javascripts/notifications_dropdown.js

 /* eslint-disable func-names, space-before-function-paren, wrap-iife, one-var, no-var, one-var-declaration-per-line, no-unused-vars, consistent-return, prefer-arrow-callback, no-else-return, max-len */
-/* global Flash */
+import Flash from './flash';
 (function() {
   this.NotificationsDropdown = (function() {

app/assets/javascripts/pipelines/components/stage.vue

@@ -13,7 +13,7 @@
  * 4. Commit widget
  */
-/* global Flash */
+import Flash from '../../flash';
 import { borderlessStatusIconEntityMap } from '../../vue_shared/ci_status_icons';
 import loadingIcon from '../../vue_shared/components/loading_icon.vue';
 import tooltip from '../../vue_shared/directives/tooltip';

app/assets/javascripts/pipelines/mixins/pipelines.js

-/* global Flash */
-import '~/flash';
 import Visibility from 'visibilityjs';
+import Flash from '../../flash';
 import Poll from '../../lib/utils/poll';
 import emptyState from '../components/empty_state.vue';
 import errorState from '../components/error_state.vue';

app/assets/javascripts/pipelines/pipeline_details_bundle.js

-/* global Flash */
-
 import Vue from 'vue';
+import Flash from '../flash';
 import PipelinesMediator from './pipeline_details_mediatior';
 import pipelineGraph from './components/graph/graph_component.vue';
 import pipelineHeader from './components/header_component.vue';

app/assets/javascripts/pipelines/pipeline_details_mediatior.js

-/* global Flash */
-
 import Visibility from 'visibilityjs';
+import Flash from '../flash';
 import Poll from '../lib/utils/poll';
 import PipelineStore from './stores/pipeline_store';
 import PipelineService from './services/pipeline_service';

app/assets/javascripts/profile/profile.js

 /* eslint-disable comma-dangle, no-unused-vars, class-methods-use-this, quotes, consistent-return, func-names, prefer-arrow-callback, space-before-function-paren, max-len */
-/* global Flash */
+import Flash from '../flash';
 import { getPagePath } from '../lib/utils/common_utils';
 ((global) => {

app/assets/javascripts/protected_branches/protected_branch_edit.js

 /* eslint-disable no-new */
-/* global Flash */
-
+import Flash from '../flash';
 import ProtectedBranchAccessDropdown from './protected_branch_access_dropdown';
 export default class ProtectedBranchEdit {
@@ -57,7 +56,7 @@ export default class ProtectedBranchEdit {
         },
       },
       error() {
-        new Flash('Failed to update branch!', null, $('.js-protected-branches-list'));
+        new Flash('Failed to update branch!', 'alert', document.querySelector('.js-protected-branches-list'));
       },
     }).always(() => {
       this.$allowedToMergeDropdown.enable();

app/assets/javascripts/protected_tags/protected_tag_edit.js

 /* eslint-disable no-new */
-/* global Flash */
-
+import Flash from '../flash';
 import ProtectedTagAccessDropdown from './protected_tag_access_dropdown';
 export default class ProtectedTagEdit {
@@ -43,7 +42,7 @@ export default class ProtectedTagEdit {
         },
       },
       error() {
-        new Flash('Failed to update tag!', null, $('.js-protected-tags-list'));
+        new Flash('Failed to update tag!', 'alert', document.querySelector('.js-protected-tags-list'));
       },
     }).always(() => {
       this.$allowedToCreateDropdownButton.enable();

app/assets/javascripts/repo/components/repo_commit_section.vue

 <script>
-/* global Flash */
+import Flash from '../../flash';
 import Store from '../stores/repo_store';
 import RepoMixin from '../mixins/repo_mixin';
 import Service from '../services/repo_service';

app/assets/javascripts/repo/helpers/repo_helper.js

-/* global Flash */
 import Service from '../services/repo_service';
 import Store from '../stores/repo_store';
-import '../../flash';
+import Flash from '../../flash';
 const RepoHelper = {
   monacoInstance: null,

app/assets/javascripts/repo/services/repo_service.js

-/* global Flash */
 import axios from 'axios';
+import Flash from '../../flash';
 import Store from '../stores/repo_store';
 import Api from '../../api';
 import Helper from '../helpers/repo_helper';
@@ -72,9 +72,9 @@ const RepoService = {
   commitFlash(data) {
     if (data.short_id && data.stats) {
-      window.Flash(`Your changes have been committed. Commit ${data.short_id} with ${data.stats.additions} additions, ${data.stats.deletions} deletions.`, 'notice');
+      Flash(`Your changes have been committed. Commit ${data.short_id} with ${data.stats.additions} additions, ${data.stats.deletions} deletions.`, 'notice');
     } else {
-      window.Flash(data.message);
+      Flash(data.message);
     }
   },
 };

app/assets/javascripts/search.js

 /* eslint-disable func-names, space-before-function-paren, wrap-iife, no-var, one-var, one-var-declaration-per-line, object-shorthand, prefer-arrow-callback, comma-dangle, prefer-template, quotes, no-else-return, max-len */
-/* global Flash */
+import Flash from './flash';
 import Api from './api';
 (function() {

app/assets/javascripts/sidebar/components/assignees/sidebar_assignees.js

-/* global Flash */
-
+import Flash from '../../../flash';
 import AssigneeTitle from './assignee_title';
 import Assignees from './assignees';

app/assets/javascripts/sidebar/components/confidential/confidential_issue_sidebar.vue

 <script>
-/* global Flash */
+import Flash from '../../../flash';
 import editForm from './edit_form.vue';
 export default {

app/assets/javascripts/sidebar/lib/sidebar_move_issue.js

-/* global Flash */
+import Flash from '../../flash';
 function isValidProjectId(id) {
   return id > 0;

app/assets/javascripts/sidebar/sidebar_mediator.js

-/* global Flash */
-
+import Flash from '../flash';
 import Service from './services/sidebar_service';
 import Store from './stores/sidebar_store';

app/assets/javascripts/star.js

 /* eslint-disable func-names, space-before-function-paren, wrap-iife, no-unused-vars, one-var, no-var, one-var-declaration-per-line, prefer-arrow-callback, no-new, max-len */
-/* global Flash */
-
+import Flash from './flash';
 import { __, s__ } from './locale';
 export default class Star {

app/assets/javascripts/task_list.js

-/* global Flash */
-
 import 'deckar01-task_list';
+import Flash from './flash';
 export default class TaskList {
   constructor(options = {}) {