Strip slashes when saving features.

[JakePT]

Description of the Change

Strips slashes from post data when saving settings. Not doing this was leading to double slashing when settings were saved to the database, which was particularly notable when using an attribute selector for Autosuggest.

Closes #2731

Alternate Designs

NA

Possible Drawbacks

NA

Verification Process

Go to ElasticPress > Features and save input[type="text"] as the Autosuggest Selector, then refresh the page. Previously the saved value would appear as input[type=\"text\"] and be double slashed as input[type=\\\"text\\\"] in the database. With this change it should show as it was entered, and only be single slashed in the database.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Changelog Entry

• Fixed - An issue where attribute selectors could not be used for the Autosuggest Selector.

Credits

Props @JakePT