Only load Premium Block CSS when that block is being used

[josephscott]

Currently when you activate the Full Site Editing plugin the style.css for the Premium Content Block gets loaded on ever page view. This change adjusts it to only load on pages where that block is being used.

Changes proposed in this Pull Request

• Only load the Premium Content Block CSS when that block is in use

Testing instructions

• Activate the FSE plugin
• Notice the Premium Content Block style.css being loaded on every page
• Apply patch
• Now style.css should only be loaded on pages that use the Premium Content Block

Fixes #

[matticbot]

Test live: https://calypso.live/?branch=premium-block-css

[matticbot]

Caution: This PR affects files in the FSE Plugin on WordPress.com
Please ensure your changes work on WordPress.com before merging.

D43853-code has been created so you can easily test it on your sandbox. See this FieldGuide page about developing in the FSE Plugin for more info: PCYsg-ly5-p2

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[gwwar]

Close, but it looks like we have some shared styling we'll need to pull out of

wp-calypso/apps/full-site-editing/full-site-editing-plugin/premium-content/style.css

Line 2 in 3372459

* The following styles get applied both on the front of your site

and into https://github.com/Automattic/wp-calypso/blob/3372459cc937cb63cf968140c10af46cc0d2ebe9/apps/full-site-editing/full-site-editing-plugin/premium-content/editor.css

Let's also update the comment at the top of style.css to note that this will be added to the published view only. @sixhours @danhauk or @Automattic/serenity @Automattic/earn any interest in helping sort styling?

Before	After

[eoigal]

I copied over the styles that were needed in the editor. The toolbar styles shouldn't have been in style.css at all so I moved those too.

[gwwar]

Thanks @josephscott for the optimization and @eoigal for the style cleanup! I verified that the editor styles look reasonable and that the published pages look good.

I did spot some minor focus changes before and after, but they both look a little off, so this is non-blocking.