Section Styles: Prevent frontend filters in admin

[aaronrobertshaw]

What?

Adds an early return for the block style variation PHP filters when in the admin.

Why?

When in either editor, a JS hook is required given the style variations applied to blocks can be changed, blocks moved around within nested variations etc.

How?

For the two filters used to process the block style variations, return early is_admin() is true.

Testing Instructions

1. Defines block style variations via the different sources below:
   • register_block_style
   • Theme.json partial file under /styles directory including blockTypes
   • Within a theme style variation under styles.variations (must be registered via either of the above two methods)
2. Check that the block style variations still apply and are displayed correctly in both editors and the frontend

Screenshots or screencast

There should be no visual changes.