Fix hiding playlist buttons from Add Media modal dialog

[erengy]

How to reproduce

On a fresh installation of WordPress 5.9.2 with ​Classic Editor plugin enabled, add the following lines to the default theme's functions.php:

<?php
add_filter('media_library_show_audio_playlist', '__return_false');
add_filter('media_library_show_video_playlist', '__return_false');

Then go to /wp-admin/post-new.php and click the Add Media button.

These filters are supposed to allow hiding the ​Create Audio Playlist and ​Create Video Playlist buttons, which is not the case. The buttons are still visible in the Add Media modal dialog.

Workarounds include filtering media_view_strings instead, or enqueing additional styles to hide the buttons.

The discussion at Ticket 43009 focuses on the behavior after uploading an audio/video file rather than the initial state, hence the new ticket.

Reason

✅ PHP: ​wp_enqueue_media function sets attachmentCounts according to the filter results.

✅ JavaScript: menuItemVisibility function is called, which adds hidden class to the elements.

❌ CSS: In media-views.css, .media-menu .media-menu-item selector wins over .media-frame .hidden, setting the elements' display property to block instead of none.

Proposed fix

Since there are similar rules of higher specificity (e.g. .attachments-browser .uploader-inline.hidden, .media-embed .setting input.hidden) in the same CSS file, I thought adding the following rule would be appropriate:

.media-menu .media-menu-item.hidden {
        display: none;
}

### How to reproduce

On a fresh installation of WordPress 5.9.2 with ​Classic Editor plugin enabled, add the following lines to the default theme's functions.php:

{{{php
add_filter('media_library_show_audio_playlist', 'return_false');
add_filter('media_library_show_video_playlist', 'return_false');
}}}

Then go to /wp-admin/post-new.php and click the Add Media button.

These filters are supposed to allow hiding the ​Create Audio Playlist and ​Create Video Playlist buttons, which is not the case. The buttons are still visible in the Add Media modal dialog.

Workarounds include filtering media_view_strings instead, or enqueing additional styles to hide the buttons.

The discussion at Ticket 43009 focuses on the behavior *after* uploading an audio/video file rather than the initial state, hence the new ticket.

### Reason

✅ PHP: ​wp_enqueue_media function sets attachmentCounts according to the filter results.

✅ JavaScript: menuItemVisibility function is called, which adds hidden class to the elements.

❌ CSS: In media-views.css, .media-menu .media-menu-item selector wins over .media-frame .hidden, setting the elements' display property to block instead of none.

### Proposed fix

Since there are similar rules of higher specificity (e.g. .attachments-browser .uploader-inline.hidden, .media-embed .setting input.hidden) in the same CSS file, I thought adding the following rule would be appropriate:

{{{css
.media-menu .media-menu-item.hidden {

display: none;

}
}}}

Trac ticket: https://core.trac.wordpress.org/ticket/55465