Fix: Cover Block: Move some editor specific styles from style.scss to editor.scss

[jorgefilipecosta]

During the reviews of #12187 we found out that the cover block contains some editor specific styles on the front end.
This is a problem because we would be transferring bytes on the frontend of websites that are not used at all.
This PR just moves this styles to editor.scss so they are loaded only in the editor.

How has this been tested?

I checked that there was no noticeable change on the cover block (and its placeholder).

[youknowriad]

Seems legit, did you try by inverting the components and block-library enqueue order?

[jorgefilipecosta]

Hi @youknowriad,
I tried to force both orders with:

--- a/lib/client-assets.php
+++ b/lib/client-assets.php
@@ -418,7 +418,7 @@ function gutenberg_register_scripts_and_styles() {
        gutenberg_override_style(
                'wp-editor',
                gutenberg_url( 'build/editor/style.css' ),
-               array( 'wp-components', 'wp-editor-font', 'wp-nux' ),
+               array( 'wp-editor-font', 'wp-nux' ),
                filemtime( gutenberg_dir_path() . 'build/editor/style.css' )
        );
        wp_style_add_data( 'wp-editor', 'rtl', 'replace' );
@@ -434,7 +434,7 @@ function gutenberg_register_scripts_and_styles() {
        gutenberg_override_style(
                'wp-components',
                gutenberg_url( 'build/components/style.css' ),
-               array(),
+               array( 'wp-block-library' ),
                filemtime( gutenberg_dir_path() . 'build/components/style.css' )
        );
        wp_style_add_data( 'wp-components', 'rtl', 'replace' );

and

--- a/lib/client-assets.php
+++ b/lib/client-assets.php
@@ -442,7 +442,7 @@ function gutenberg_register_scripts_and_styles() {
        gutenberg_override_style(
                'wp-block-library',
                gutenberg_url( 'build/block-library/style.css' ),
-               current_theme_supports( 'wp-block-styles' ) ? array( 'wp-block-library-theme' ) : array(),
+               current_theme_supports( 'wp-block-styles' ) ? array( 'wp-block-library-theme', 'wp-components' ) : array( 'wp-components' ),
                filemtime( gutenberg_dir_path() . 'build/block-library/style.css' )
        );
        wp_style_add_data( 'wp-block-library', 'rtl', 'replace' );

Things worked as expected in both cases.

[youknowriad]

Thanks for the tests