Release testing instructions: Storefront 3.8.0

Remove skip-link-focus-fix.js (#1653)

1. Open any StoreFront page in Safari (which is the only major browser using webkit).
2. Tab to skip link.
3. Press Enter to activate it.
4. Make sure keyboard focus has moved to the first focusable area.
5. Repeat this process for Opera and the other major browsers.

Minor edits to readme (#1711)

1. Read the readme to see if it makes sense.

Remove full width image mobile margin and remove full width image block margins on mobile (#1713)

1. Add an Image block to a new page, set it to full width;
2. Make sure the page's template is also set to Full Width, and save/publish the changes;
3. Open the created page on a browser with at least 1064px width. Verify that the image is full width.
4. Switch to browser responsive mode and reduce the screen size to 1063px width or less. Verify that there are margins on both sides.

Fix hidden disclosure arrow on <summary> tags (#1727)

1. Create a page with a custom HTML block containing the following markup:

<details>
  <summary>Summary</summary>
  <ul>
    <li>Details</li>
    <li>Details</li>
    <li>Details</li>
</ul>
</details>

2. The summary should show, complete with a disclosure arrow to indicate that it is expandable:

Removed superfluous slashes from Star and WooCommerce fonts urls (#1754)

1. View the source of your website, and find star.eot
2. Check if the url contains a duplicate slash
3. Check if all icons are displayed properly

Prevent search widget styles leaking into the Search block when added to a widget area (#1755)

1. With WordPress 5.8, go to Appearance > Widgets.
2. Add the Search block into the sidebar.
3. Go to the frontend, and verify there isn't a magnifier icon which overlaps the label:

Before	After

4. Try toggling some attributes of the Search block and verify it's displayed as expected in the frontend.