Move max MR files to open count to constant

- Previously this was just a magic number
- Now its encapsulated

app/assets/javascripts/ide/constants.js

@@ -107,3 +107,7 @@ export const SIDE_RIGHT = 'right';
 
 // Live Preview feature
 export const LIVE_PREVIEW_DEBOUNCE = 2000;
+
+// This is the maximum number of files to auto open when opening the Web IDE
+// from a Merge Request
+export const MAX_MR_FILES_AUTO_OPEN = 10;

app/assets/javascripts/ide/stores/actions/merge_request.js

 import { deprecatedCreateFlash as flash } from '~/flash';
 import { __ } from '~/locale';
-import { leftSidebarViews, PERMISSION_READ_MR } from '../../constants';
+import { leftSidebarViews, PERMISSION_READ_MR, MAX_MR_FILES_AUTO_OPEN } from '../../constants';
 import service from '../../services';
 import * as types from '../mutation_types';
 
@@ -152,7 +152,9 @@ export const openMergeRequestChanges = async ({ dispatch, getters, state, commit
     .map((change) => ({ entry: state.entries[change.new_path], change }))
     .filter((x) => x.entry);
 
-  const pathsToOpen = entryChanges.slice(0, 10).map(({ change }) => change.new_path);
+  const pathsToOpen = entryChanges
+    .slice(0, MAX_MR_FILES_AUTO_OPEN)
+    .map(({ change }) => change.new_path);
 
   // If there are no changes with entries, do nothing.
   if (!entryChanges.length) {

spec/frontend/ide/stores/actions/merge_request_spec.js

 import MockAdapter from 'axios-mock-adapter';
 import { range } from 'lodash';
-import testAction from 'helpers/vuex_action_helper';
 import { TEST_HOST } from 'helpers/test_constants';
+import testAction from 'helpers/vuex_action_helper';
 import { deprecatedCreateFlash as createFlash } from '~/flash';
-import { leftSidebarViews, PERMISSION_READ_MR } from '~/ide/constants';
+import { leftSidebarViews, PERMISSION_READ_MR, MAX_MR_FILES_AUTO_OPEN } from '~/ide/constants';
 import service from '~/ide/services';
 import { createStore } from '~/ide/stores';
 import {
@@ -395,7 +395,7 @@ describe('IDE store merge request actions', () => {
         (acc, { path }) => Object.assign(acc, { [path]: path, type: 'blob' }),
         {},
       );
-      const pathsToOpen = changes.slice(0, 10).map((x) => x.new_path);
+      const pathsToOpen = changes.slice(0, MAX_MR_FILES_AUTO_OPEN).map((x) => x.new_path);
 
       return testAction({
         action: openMergeRequestChanges,

spec/frontend_integration/ide/user_opens_mr_spec.js

 import { basename } from 'path';
-import { useOverclockTimers } from 'test_helpers/utils/overclock_timers';
 import { getMergeRequests, getMergeRequestWithChanges } from 'test_helpers/fixtures';
+import { useOverclockTimers } from 'test_helpers/utils/overclock_timers';
 import * as ideHelper from './helpers/ide_helper';
 import startWebIDE from './helpers/start';