Lint fixes

[oscarssanchezz]

Description of the Change

• Introduces a global color CSS file to reuse common colors on different stylesheets.
• Fixes PHP lint issues
• Fixes JS lint issues
• Fixes Style lint issues

Closes #4041

How to test the Change

Linting:

Run

• composer run lint
• npm run lint-js
• npm run lint-style

All of them should pass.

ElasticPress functionality

• Functionality should be the same, with minor visual changes.

Changelog Entry

Developer - PHP, JS and Style lint fixes.
Changed - ElasticPress\Feature\RelatedPosts::get_related_query(), ElasticPress\Feature\RelatedPosts::find_related() parameter name change to $post_return

Credits

Props @oscarssanchezz, @felipeelia

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.