Indentation within HTML block with empty lines

[fonsp]

The following input:

asdf

<blockquote class="banner">
    <p>Hello world.</p>
</blockquote>

produces this output:

<p>asdf</p>

<blockquote class="banner">
    <p>Hello world.</p>
</blockquote>

---

but if I add an empty line inside the block, the contents get escaped: 😥

asdf

<blockquote class="banner">

    <p>Hello world.</p>
</blockquote>

<p>asdf</p>
<blockquote class="banner">
<pre><code>&lt;p&gt;Hello world.&lt;/p&gt;
</code></pre>
</blockquote>

[MichaelHatherly]

If we're inconsistent with https://spec.commonmark.org/dingus/ then we can adjust as needed, but I think we are probably replicating the expected behaviour of the reference implementation here.