Changes proposed in this Pull Request:

• Update the Amazon, Calendly, Google Calendar, and OpenTable blocks to use the withNotices HOC instead of manually handling the error notices.

Pros: it's the Core Gutenberg way of handling placeholder notices; manual notices are incorrectly positioned on recent Gutenberg versions (see #14833 for a CSS-only fix).

Cons: notices created with withNotices are always dismissable, while all our manual notices aren't. I don't think it's a big deal to be honest.

Note

Other blocks already use the withNotices HOC, but some in a slightly peculiar way.
According to the Gutenberg docs, withNotices exposes a noticeUI prop that is passed to the Placeholder through the notices prop.
E.g.

<Placeholder notices={ props.noticeUI } />

Some blocks instead use the noticeUI outside the Placeholder (the notice would appear above the block content—but still inside its container), while passing a notices prop to the Placeholder notices prop.
E.g.

<Fragment>
  { props.noticeUI }
  <Placeholder notices={ props.notices } />
</Fragment>

I'm not exactly sure why this happens, and for example why this doesn't end up displaying two notices, one in the Placeholder, and one above the block content.
I've chosen to not touch these blocks, to avoid unexpected regressions.

Testing instructions:

• Insert the Amazon, Calendly, Google Calendar, and OpenTable blocks, and try triggering an error notice by inserting an incorrect URL or embed code.
• Make sure the notice still works and is positioned consistently.

Proposed changelog entry for your changes:

• Update the Amazon, Calendly, Google Calendar, and OpenTable blocks to use the withNotices higher-order component.