E2E Compatibility Refactor

[AnthonyLedesma]

Refactor tests and helpers to support the expected features of WP 5.4 (or Gutenberg 7.2) and is compatible with and without the Gutenberg plugin active.

ESLint

• Applied ESLint to all tests and helper.js.
• Installed Cypress ESLint plugin.
• Removed tests from .eslintignore

helper.js

• Added logic to deprecate core/nux into select( 'core/edit-post' ).isFeatureActive( 'welcomeGuide' )
• Enhanced selector specificity with Regex to click the appropreate elements.
  • Resolves issues where referenced classes have been deprecated.
• Identified and implemented alternate solutions for Cypress changes around getBlockSlug function.
  • Cypress.spec.name is not as expected in certain scenarios.
  • Cypress.spec is incorrect when running all specs, should contain actual current spec cypress-io/cypress#3090

**.cypress.js

• Re-wrote logic around setting Font Sizes for cross-version compatibility.
• Adjusted functions to pass the appropriate slug.
  • IE helpers.addCoBlocksBlockToPage( true ); changed to helpers.addCoBlocksBlockToPage( true, 'accordion' );

[EvanHerman]

Nice work @AnthonyLedesma 👏! Things look good to me, are still working well on my end and tests are all passing.