Add styles for callouts to match notice blocks

[adamwoodnz]

Fixes #428

Adds styles matching the mu-plugins notice block as a temporary fix until we can support GitHub markdown.

Removing these old styles also means we can remove the dashicons style dependency unless we're on the dashicons page or the Code Comment bloc is rendered. The dashicon styles are already loaded if logged in.

Screenshots

Before	After

Testing

Callouts

Visit pages using callout markup:
http://localhost:8888/block-editor/contributors/documentation/#callout-notices
http://localhost:8888/block-editor/getting-started/devenv/
http://localhost:8888/block-editor/getting-started/devenv/get-started-with-wp-env/

Check that callouts match the design.

Dashicons

Visit the homepage and check that dashicons.css and editor.css are not loaded.

Visit http://localhost:8888/resource/dashicons/ and check that dashicons.css is loaded and the icons are displayed as expected.

Visit http://localhost:8888/reference/classes/wp_query/ and check that editor.css and dashicons.css are loaded. There was a bug with editor and dashicons styles not loading when there are multiple comment forms loaded. Test the link button in the comment rich text editor, it should open a modal. Check that this still works with 1 comment and multiple.

[renintw]

Tested and all look as described 👍

Except for a couple of minor things:

Saw that either in
https://www.figma.com/file/2WxlJFzMJvqPfZL1EkAOVp/Developer-Resources?type=design&node-id=3735-20039&mode=design&t=hFLJ9Js5ydN24rhe-0
or
https://www.figma.com/file/HOJTpCFfa3tR0EccUlu0CM/WordPress.org-Design-Library?type=design&node-id=1264-4116&mode=design&t=X6mkiADJtXl6S0GO-0
the font size for callout content is 14px.

--

And I still can see dashicons.css being loaded on the homepage. editor.css indeed isn't loaded.

Not really a blocker IMO.

[ndiego]

the font size for callout content is 14px.

Yeah, I think the font-size should be set to --wp--preset--font-size--small.

And I still can see dashicons.css being loaded on the homepage. editor.css indeed isn't loaded.

I think dashicons are always loaded by default on WP sites, so might just be that.

Looking great though! 🙌

[adamwoodnz]

And I still can see dashicons.css being loaded on the homepage. editor.css indeed isn't loaded.

Yeah could be a couple of reasons for this; it's loaded if you're logged in (for the admin bar), and frontend loading seems to have changed in WP recently, as we had to patch some sites to force load it, so it could depend on your WP version.