Enhancement: Format and sanitize the layout of the fields attribute

[andrewlimaza]

The fields attribute in the shortcode and block editor can be incorrectly configured. A comma where there isn't suppose to be one, or a space between comma's causing malfunctions.

The general overview is to sanitize and validate the format of the fields attribute.

Here is a gist to remove spaces between the comma values of the fields attribute: https://gist.github.com/ipokkel/17266debaf7eeb3f349de1392be473e6