Add helpers for HTML fixtures to Jest

Inactive Accountrequested to merge
winh-jest-html-fixtures into master

What does this MR do?

Provides helper functions to load HTML fixtures in Jest tests similar to Karma.

What are the relevant issue numbers?

closes https://gitlab.com/gitlab-org/gitlab-ce/issues/57998

Before

FAIL spec/frontend/pages/admin/abuse_reports/abuse_reports_spec.js
  ● Abuse Reports › encountered a declaration exception

    ReferenceError: preloadFixtures is not defined

      15 |     $messages.filter((index, element) => element.innerText.indexOf(searchText) > -1).first();
      16 | 
    > 17 |   preloadFixtures(FIXTURE);
         |   ^
      18 | 
      19 |   beforeEach(function() {
      20 |     loadFixtures(FIXTURE);

      at Suite.preloadFixtures (spec/frontend/pages/admin/abuse_reports/abuse_reports_spec.js:17:3)
      at Object.describe (spec/frontend/pages/admin/abuse_reports/abuse_reports_spec.js:5:1)

(https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/186304544)

After

PASS spec/frontend/pages/admin/abuse_reports/abuse_reports_spec.js

(https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/186315765)

Does this MR meet the acceptance criteria?

Edited by Inactive Account

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