feat: [FC-0070] add message events and styles to the library content page (#35785)

This introduces improvements for XBlock interactions within iframes:

* Add default styles for Library Content that renders in the iframe in the new Studio unit page
* When the `isIframeEmbed` option is enabled, the XBlock sends a `postMessage` to the parent window. When sending such a message, the standard link transition is cancelled and the transition is carried out in the MFE.

cms/templates/studio_xblock_wrapper.html

@@ -229,7 +229,7 @@ upstream_info = UpstreamLink.try_get_for_block(xblock)
             <div class="meta-info">${_('This block contains multiple components.')}</div>
             <ul class="actions-list">
                 <li class="action-item action-view">
-                    <a href="${xblock_url}" class="action-button">
+                    <a href="${xblock_url}" class="action-button xblock-view-action-button">
                         ## Translators: this is a verb describing the action of viewing more details
                         <span class="action-button-text">${('View')}</span>
                         <span class="icon fa fa-arrow-right" aria-hidden="true"></span>